Fundamentals of environmental testing

Technology Report

Fundamental Concepts of Environmental Testing
Techniques in Electricity and Electronics
Part 1: Fundamental concepts of physics and chemistry regarding heat and humidity
Toshio Yamamoto

T

ESPEC CORP. Environmental Test Technology Center

his article is the first in a four-part series on basic issues concerning reliability
and quality control in electricity and electronics. The issues to be covered deal
mainly with “temperature and humidity testing”, and are primarily directed

toward beginning technicians who are participating in environmental testing.
The series is organized as follows:Part 1: Fundamental concepts of physics and chemistry regarding heat and humidity
Part 2: Concepts concerning the behavior of standard environments and moisturerequired for designing temperature and humidity tests
Part 3: Concepts concerning the establishment of public test standards
Part 4: Concepts serving as reference for effectively applying environmental testing
The aim of this series is to present the fundamental concepts required for performing
temperature and humidity testing, the most basic testing in the various kinds of test
methods. In addition, we sincerely hope that these fundamental concepts will lay thefoundation for understanding current environmental tests, designing the next
generation of environmental tests, and developing new test methods.

1 Introduction
Fifteen years ago in Japan, the electrical and electronics industry used “environment”
to refer to natural environments. Nowadays, though, the term is used to include othermeanings. The rapid development of industrial technology has widely popularized agreat variety of industrial products which have provided enormous convenience in ourlives. However, this situation is also leading to immense changes in the naturalenvironment on a global scale. It is well-known that these changes are giving rise to avariety of current social problems.
Modern industrial products have increasingly numerous opportunities to be directly
and strongly influenced by environmental changes, including naturally occurring
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periodic weather changes such as the changing seasons, and the environment of thegeographical location, but even more by artificial environmental changes brought about
by environmental changes in the rooms in which the products are placed, as well as bynon-periodic operation of other products located close by. In other words, the influenceof the artificial interior environment has become greater than the influence from theglobal natural environment. (Our own bodies are also receiving the effects of this sameenvironmental influence on a daily basis.)

2 Physical properties of temperature and humidity
Temperature refers to thermal energy, and we can only grasp the level of thermalenergy through some sort of matter. In other words, thermal energy is not matter.
Because of this, we use appropriate instruments (thermometers and calorimeters) toindex the order of coolness and heat and its increase and decrease, i.e. the amount ofthermal energy and the level of change in that energy.
Humidity is a combination of water and dry air, and the water can easily change into avariety of forms within our life temperature zone. Occasional high and low
temperatures cause the humidity values to fluctuate widely.
We know from experience that when a hot substance comes into direct contact with acold substance, the hot one cools and the cold one warms. This change does not continue
in perpetuity, but is rather one that reaches equilibrium after time, and the change
stops. At this time the two substances involved are said to have reached thermal
equilibrium. We should also note that as the temperature of a substance increases,
molecular motion correspondingly increases in the molecules composing the substance.
However, as the temperature drops, molecular motion also slows. It is well known thatat extremely low temperatures, in the vicinity of –273°C, molecular motion in most
molecules stops.
2.1 Molecular motion of gases
Fig. 1 illustrates the velocity of one oxygen molecule in a vacuum. As the temperaturerises, the velocity increases. In other words, the higher the temperature of a gas, thegreater the kinetic energy that it has (the thermal motion of the molecule increases).

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25°C

100°C

At 25°C, velocity is

At 100°C, velocity

approximately

is approximately

440m/s

490m/sFig.1 Velocity of one molecule of oxygen
Next, let’s observe the molecular motion of groups of molecule.
2.1.1. With groups of identical molecules
Even when a number of identical molecules form a gas, the velocity of all the molecules
making up the gas is not equal. Each of the molecules conforms to the uniform velocity
distribution (1) determined by the temperature. As Fig. 2 clearly shows, the higher thetemperature, the more the distribution is inclined toward an area of greater velocity.
For example, the velocity distribution of N2 molecules in nitrogen gas is as shown in Fig.
2. When most of the molecules are temporarily at the average velocity v for thattemperature, the value of v for the N2 molecules changes to 425 m/s at 0°C, 910 m/s at
1,000°C, and 1,220 m/s at 2,000°C.

Fig.2 Temperature and distribution of molecular velocity
2.1.2. With groups of different type of molecules
Even at the same temperature, the velocity distribution of groups of molecules withlower molecular weight has a distribution more inclined toward an area of greater
velocity than groups of molecules with greater molecular weight. For example, whencomparing hydrogen molecules (molecular weight, 2) with nitrogen molecules
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Fundamentals of environmental testing(molecular weight, 28) as in Fig. 2, at the same temperature of 0°C, the velocity v of theH2 molecules is 1,680 m/s, but the velocity v of the N2 molecules is 425 m/s.
The higher the temperature, the greater the average molecular velocity v is. This valueof v is known to be in proportion to the square root of absolute temperature T. The
average velocity can be found with the following formula, in which M is the molecularweight.

V=

√3RT
M

(Where R is the gas constant)

This type of temperature change creates thermal stress by changing the velocity
distribution of the molecules composing the substance that is in thermal equilibrium,i.e., stable. Therefore, changing the temperature of a substance causes repeatedchanges in velocity at the molecular level, so the substance is not static even though its
macro stability can be observed. From the micro standpoint, a substance is normally inan unstable condition. The greater the change in temperature, the greater the loss ofstability is. To put it the other way around, the smaller the change in temperature, thegreater the relative stability is.
Next, let’s consider humidity. When dealing with the subject of moisture content, theprerequisite for humidity, we must bear in mind the characteristics of water. Water is
at its greatest density at 4°C (1 atm, 3.98°C), and undergoes phase changes according to
the temperature. In other words, depending on the temperature, water will exist as
water vapor (gaseous phase), water (liquid phase), or ice (solid phase). Within our life
temperature zone we don’t often see liquids freeze (with the exception perhaps of only
glacial acetic acid (2) and benzol (3)).
By the way, when discussing phase change, we must not forget the existence ofintermolecular force.
First of all, when a gas is cooled or compressed, it becomes a liquid (in rare instanceschanging directly to a solid). For example, when air is compressed and cooled, it
becomes liquid air, and when carbon dioxide is cooled, it becomes a snow-like solid (dryice). These phenomena indicate that the molecules attract each other. This force iscalled intermolecular force, or Van der Waals force (Van der Waals, 1837 to 1923). This
intermolecular force is created only when molecules are contiguous, and is rarely
created when the intermolecular distance is great. Therefore, in solids and liquids,
intermolecular force results in molecules being held almost immobile or merely able toflow. When the substance becomes a gas, the molecule can fly about almost freely(Although within the range of mean free path (4)). For example, butane (C4H10) boils at
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10°C, and at room temperature is a gas, but is a liquid in a gas lighter. This is because
the butane is compressed and put into the lighter, forcibly reducing the intermoleculardistance between the butane molecules. This compression creates intermolecular force,
forming a liquid and making it possible to insert 200 times as much butane into thelighter.
Butane (boiling point -0.5°C),
is approx. 22.4L at 0°C and1atm (gas), and in cubic form
one side is 28.2cm. As a liquid
at 0°C and 1atm, it is approx.
97ml and in cubic form one
side is 4.6cm. Therefore theintermoleculardistance

inthe gaseous phase is 6 times
the liquid phase (28.2/4.6)

Fig.3 1 mol of butane (liquid and gas)

Fig.4 Intermolecular distanceIntermolecular force is strongly affected by intermolecular distance, and is inversely
proportional to the intermolecular distance raised to the power of 7. For example, if theintermolecular distance is doubled, the intermolecular force becomes 1/27, i.e., 1/128.
Intermolecular distance is a weaker force than chemical bonds (ionic bonds (5), covalent
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bonds (6), and metallic bonds (7)), but it is incomparably stronger than universal gravity.
However, coming too close together creates repulsion force, so molecules can’t approachcloser than a certain uniform distance. The atomic radius determined from this distanceis called the Van der Waals radius, which is considerably larger than the covalent bondradius.
We don’t have room to go more into detail on this subject here, so if you would like toknow more about it, please refer to other sources.
Incidentally, water undergoes a change in volume when changing from a liquid to agaseous phase or to a solid phase, and because of that exerts an extremely strong
mechanical force on its surroundings. Also, existing at the boundaries of the various
changes are special characteristics such as the appropriate gain and loss of kinetic
energy as latent heat (8) in cases in which there is no temperature change. Anothercurrent problem is that even when the amount of moisture is insufficient to cause
problems as independent water, when combined with other major factors it can form acomplex environment with properties that severely affect electrical and electronic
products.
2.2 Vaporization and expansion
Heated water evaporates and becomes water vapor in a phenomenon known as
evaporation, but this process change from the liquid phase to the gaseous phase isaccompanied by expanding volume, a phenomenon known as evaporative expansion.
According to the Ideal Gas Equation on the relationship between the temperature andpressure of a gas, when this expansion occurs in a closed system, the internal pressureof the system increases in proportion to the temperature. For example, at 0°C and 1 atm,
1 cm3 of water becomes 1.24 L when vaporized, in other words, it expands to 1,240 times
its liquid volume. This phenomenon is shown in the following manner:
The Ideal Gas Equation
PV = nRT
We can substitute the following values:
P = 1 atm
R = 0.082 atm/°C · mol
T = 273°C, andn = 1/18 mol/gm
in the following formula:V = nRT/P
to confirm that the result is 1.24 L.

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For example, when water (liquid) 18 cm3 evaporates, it becomes:
vaporizes
Water (liquid)water vapor (gas)18 cm3 (gm)

22.4 L

2.3 Freezing and expansion
Volume expansion due to freezing occurs on a very small scale compared to vaporization
expansion, and it also relies much less on temperature. When 1 cm3 of water freezes at
0°C and 1 atm, the volume becomes 1.09 cm3, a 1.09 times increase. This value can befound in the following manner. The density of water at 0°C and 1 atm is 1 gm/cm3, so thevolume of 1 cm3 of water has a weight WL of 1 gm. When this freezes, at 0°C and 1 atm,the density ds of ice = 0.917 gm/cm3, so the volume can be found as follows:

Vs =

WL
ds

= 1.09cm3

In other words, when 1 cm3 of water (liquid) freezes:
freezing
Water (liquid) 1 cm3

ice (solid) 1.09 cm3
1.09 times

The reason for this freezing expansion is as follows.
Within liquid water are groups of water molecules that are linked together by hydrogenbonds (bonds formed when the positively charged H atoms in the molecules form mutual
electrostatic attractions with negatively charged atoms in other molecules, in this caseoxygen atoms). When the temperature drops, the thermal motion of water decreases
and the groups become larger, and at around 0°C most of the water molecules are linked
by hydrogen bonds. Then, as the temperature drops below 0°C, the water molecules lose
the ability to move freely, becoming crystallized. Therefore, the water molecules in ice
form an orderly crystal lattice. This crystalline structure contains a large number ofgaps, and so the volume occupied is greater than water. Most substances become denser
as the temperature drops and less dense as the temperature rises. (Temperature isinversely proportional to density, forming the basis for the use of substances such as
alcohol or mercury in thermometers.) This property of water differs from othersubstances, and is an exception to the general rule that the solid phase is less dense.
When ice melts and water molecules become able to move, molecules are able to enter
the gaps causing water to become denser, and so ice is able to float. (Example, icebergs)
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Expressing the existence of water as humidity refers to the amount of water vapor in
the air. The unit of humidity generally used as an environmental factor inenvironmental testing is called relative humidity, which is based on the capacity
standard. Relative humidity is defined by the following formula:

e

RH =

( E ) x100 (%)

Where,
RH = relative humidity,e = the moisture content actually present of the air’s uniform capacity at the uniform
temperature, andE = the maximum moisture content possible at the temperature condition in e, at thesaturation moisture content in the air.
This moisture content is also shown in proportion to a certain water vapor pressure.

3 Chemical properties of temperature and moisture
Thermal energy, the index of temperature, is not matter so it is not directly involved inchemical reactions. Thermal energy can penetrate or leave matter. It can come into
being and be extinguished inside matter, and can intensify or calm the motion ofmolecules forming matter. It can effectively speed or slow chemical reactions. At thesame time, chemical reactions occurring inside matter can create new thermal energy or
exhaust thermal energy as a product of the reaction. However, when the reacting
substances of a chemical reaction are consumed, the reaction will stop regardless oftemperature. Thermal energy plays a supporting role in relation to moisture, but themain role in this domain is the moisture itself, and its absolute mass. Most chemical
reactions occur in solvents, so we can assume that water molecules play some sort ofrole.
3.1 The structure of the water molecule
The water molecule has an extremely wide variety of functions. We have already notedthat the state of water changes according to the temperature. The water molecule iscomposed of one oxygen atom and two hydrogen atoms. The structure forms atetrahedron with the oxygen atom at the center, and the hydrogen atoms receiving thetwo electrons from the oxygen atom are at the two peaks, i.e., the location of the protons.
The distance between the center of the hydrogen atoms and the center of the oxygen
atom is approximately 10–10 m (1.0Å), and the two hydrogen atoms enclose the oxygen
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atom at an angle of approximately 105°.

Fig. 5 The structure of water
3.2 Properties of water
The more pure the water, the lower its ability to conduct electricity, but regardless of
how much it is purified, water will always have some level of conductivity. This isbecause an extremely small amount of H2O ionizes into H+ and OH– and maintains
ionization equilibrium as shown in the following formula:

H2O = H+ + OH–
This ionization equilibrium is not only true for pure water, but also holds true for waterin aqueous solutions of acids, bases, salts, and so on. This relationship can be shownusing the equilibrium constant. In pure water and weak aqueous solutions therelationship can definitely be seen as constant, and can be described with the following
formula:[H+] [OH–] = K [H2O] = Kw
This Kw is called the ionic product of water, and is a constant that changes according to
the temperature. This constant value is always maintained in any sort of aqueous
solution, whether pure water, acid, base, salt or other. In pure water it is [H+] = [OH–].
By measuring the electrical conductivity of pure water, this value can be established as
1.0 x 10–7 mol/L at 25°C. Putting this value in the above formula gives us
Kw = [H+] [OH–] = (1.0 ´ 10–7 mol/L)2 = 1.0 x 10–14 mol2/L2
However, as we have already noted, the ionic product changes according to temperature
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and the higher the temperature the greater the value of the ionic product.
Furthermore, as a property of water, one molecule has the same characteristics as one
drop or one cup of water (a giant molecule). Also, ions such as the hydrogen ion H+ andthe hydroxide ion OH– have an extremely high mobility ratio. In other words, H+ and[H3O]+ (oxonium) ions move toward the cathode, and the OH– ions move toward theanode.
Water is generally very good at dissolving ionic compounds, but at room temperature
reacts with metals such as sodium, potassium, and calcium. Water vapor reacts withiron to create hydrogen and form oxides and hydroxides, and hydrolyzes with
substances such as nonmetallic halides and esters. (Hydrolysis is dissolution inside themolecules that compose the substance, i.e., changing the bonds inside the molecules.) A
comparatively large number of substances react in this way.

4 Activation state and activation energy
When dealing with the problems of failure analysis and life of electrical and electronicparts, attention repeatedly focuses on activation energy. This is because thedegradation of part functions is deeply related to the manner in which the chemical
reaction proceeds.
4.1 What is activation state?
We stated in section 2-1 that the distribution of kinetic velocity (kinetic energy) of gas
molecules inside a container is uniform in response to that temperature. We further
noted that if the temperature of the gas inside the container is raised, the kinetic energyof the molecules tends to be greater. These phenomena are intimately related to thechemical reaction of matter. For example, even if iodine (9) is put into the container andleft at room temperature, a decomposition reaction does not occur, but with atemperature of 400°C a decomposition reaction occurs as shown by the following
formula:2HI

H2 + I2

In general, when the temperature of a gas is raised:a) Molecular motion becomes more energetic, and the collision frequency of themolecules inside the container increases.
b) As the kinetic energy of the molecules increases, when they collide there isan increased probability of rearranging the connections between the atoms.
(This is chemical reaction.)
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The molecules that have collided don’t all react. Within the particles of the reactants(such as ions and molecules) only the particles above the uniform energy react. To makeall the remaining particles react, more energy would have to be applied. (Refer to Fig. 6)

Fig.6 Energy of particles able to react
For a reverse reaction, let’s look at the process that produces hydrogen iodide (HI).
When high energy molecules collide in the direction shown in Fig. 7, a reaction isstarted. In this case, the H2 molecules and I2 molecules don’t react directly. They firstpass through an intermediate state in bonding as 2 molecules of HI.
I2 + H2[intermediate state]

2HI

Fig.7 Model of the activated stateThis intermediate state has more energy than the average energy of the original
reactants (the H2 and I2 molecules). Once this state has been reached, energy is
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immediately released and the molecules become stable product molecules (HI). This
intermediate state is called the activating state. The dissolution of 2HI that we
discussed earlier must also pass through this activated state. In chemistry, this type ofintermediate body is called an activated complex.
4.2 Activation energy
In the reaction A + B = AB + QkJ in Fig. 8, the energy (Ea) required to activate all
reactants (A + B) to condition X is called the activation energy. In other words, thedifference between the energy of the reactants and the energy of the activated state is
the activation energy. This X immediately releases energy (Eb) and becomes a product(AB). In other words, it is also the activation energy of the reaction AB

A + B. In thiscase, Q corresponds to added heat from outside that can raise the constant energy of theparticles not yet having reached a reactive level to such a level at which they can react.
This indicates that reactants in chemical changes must generally cross the peak ofactivation energy before they can become products.

For H2 + L2 = 2HI(Reference: The energy required to separate

Eb = 184 kJ

2 molecules of H and 2 molecules of I is

Ea = 171 kJ

approximately 587 kJ, but since theQ = 13 kJ

reaction proceeds at 171 kJ, it is obviousthat the reaction is not between the atoms.)

Fig.8 Activation energy
4.3 The role of temperature in reaction state
When an aqueous solution of sodium hydroxide (caustic soda) is added to hydrochloric
acid, a neutralization reaction occurs, but this reaction is so extremely fast that it ends
the instant that it is mixed. On the other hand, reactions involving the rusting of iron
spikes and copper plates proceed slowly over a long time. However, the speed at which
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Fundamentals of environmental testingchemical reactions proceed depends on the type of reaction. Even with the same type ofreaction, the reaction rate will vary depending on the reacting substances and thereactant states.
The reaction rate can be shown either in units of time of the rate at which the reactants
are used up, or the rate at which the products increase. Either way, the relationship is
as follows:[Reaction rate] = [proportional constant] x [density of reactant or product]
The proportional constant is determined by the temperature, and the formula thatshows this relationship between the reaction rate and density is called the rate equation.
In general, the higher the temperature the faster the reaction rate. For example, if thetemperature rises 10°C the rate constant becomes 2 or 3 times greater, so such
expressions as the 10°C rule are used. In 1889, the Swedish physicist Arrhenius
discovered the linear relationship between the logarithm of the rate constant K (log K)
and the inverse number (1/T) of the absolute temperature T (= 273+t°C) as shown in Fig.
9. This relationship is quite often used in failure analysis when analyzing chemical
reactions between substances and when calculating the rate constant.

Log kLarger rate
constant

Higher temperature

1
T
Fig.9 Relationship between the rate constant and temperature
The explanation given above forms the basis for the thermal stress and humidity stresstests that we perform, and is intimately related to the failure of many products. In theactual market environment, many electrical and electronic products fail due to physicaldistortion caused by differences in the amount of thermal expansion between materials
used to construct the product. As a result, gaps are left at the interface of materials with
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different coefficients of thermal expansion, and in extreme cases cracks are introduced
into sealing material made of the same material. Moisture can penetrate through thesecracks or through the surface of the material through long contact. As the moisture
contacts the passageway it dissolves a variety of contaminants from the materialinterface, and as the water gets mixed in, it reaches the inner electrical circuits. At thispoint it reacts chemically with the materials forming the circuits.
Furthermore, electrical current and electrical and magnetic fields strongly recreate
these reactions. The reactions are also strongly affected by temperature. In this way wecan see that failure results from purely physical phenomena and chemical reactions
occurring repeatedly at the same time and creating complex stress. When physicalcauses and chemical causes occur in succession or together, the related phenomena
speed degradation of the product. If the durability of the product is exceeded, this canlead to cessation of functions and product failure.

5 Accelerated testing of temperature and humidity
In the initial stages of its development, environmental testing was used to perform
simulation testing of the earth’s natural environment. However, current environmental
testing has come a long way from the original simulation testing, and that change is due
to artificially accelerated testing. According to IEC 50 (191), an accelerated test is
explained as “A test in which the applied stress level is chosen to exceed that stated in
the reference conditions in order to shorten the time duration required to observe thestress response of the item, or to magnify the response in a given time duration.”
However, it would be rash to decide that trustworthy reliability for the market
environment has been established merely on the basis of products having endured a test
that is more severe than the standard conditions. In fact, products that have passed
extremely rigorous test conditions have occasionally been found to fail in quite mild
environments. For example, when only temperature stress is applied to ester resins
such as polyester and carbonate they show a life of tens of thousands of hours even at
150°C. When the coefficient of water absorption is also in the range of 0.1 percent,moisture absorption causes almost no changes in the substance. However, whentemperature and humidity are applied at the same time, for example, an item that has a
27-year life at conditions of 20°C and 100% RH has a life of just three days at 35°C and100% RH. In addition, if metallic ions and alkali ions are present during hydrolysis, or if
copper transition elements and pigment are present during polypropylene oxidation
decomposition, these kinds of substances indicate the action of an acceleration catalyst,
and decomposition occurs rapidly in this situation.
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When planning a test, one must grasp the appropriate details of stress, and fullycomprehend the results of such matters as the types and individual combinations ofstress. One should be well aware that merely increasing the severity of test conditions
does not produce accelerated testing.

6 SummaryFirst of all, from the qualitative standpoint, product failure begins with the causes that
degrade the characteristics of materials used in a product, combined with external
physical and chemical causes. Next, we consider influences from the product itself andfrom a variety of environments in its surroundings that speed degradation and cause
substances that react to be consumed, causing early degradation or cessation of productfunctions. A number of factors can cause product failure, but among them the mostfundamental region of study concerning reliability of electrical and electronic products
concerns phenomena originating in temperature and humidity (moisture content).
The matter of actually handling environmental testing as a job entails confirming
product endurance under test conditions, exposing product weaknesses as early as
possible, and correcting those weaknesses. Naturally, after the product has been
improved, confirmation testing must be carried out. For these reasons, this discussionin Part 1, as well as in the follow-up articles, focuses thoroughly on acquiring the basic
knowledge of physics and chemistry as well as knowledge about test standards.
This basic knowledge and experience is essential for providing a basis for further
learning. Also, in the area of test design, ability to fully predict the details of failure andthe mechanisms leading to failure before testing makes it possible to create a more
effective test. Our theme in the next issue will be “Fundamental concepts of thestandard condition and movement of water or moisture for performing temperature andhumidity tests”, and we will be discussing standard environments, thermal stress,
humidity stress and their relationship to electrical and electronic product failure.
Glossary(1). Velocity distribution:
It used to be thought that when the temperature of a group of the same type ofmolecules was equal, their velocity would also be equal, but this can only be said of theaverage velocity of the individual molecules. A distribution curve of the velocity for agiven instant is shown in Fig. 2. (The work of Maxwell, England, 1860, and Boltzmann,
Austria, 1868 led to this conclusion.) This distribution is caused by changes in velocity
when the molecules frequently and incessantly collide with each other. (Reference: The
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Fundamentals of environmental testinghigher the temperature, the lower the velocity distribution peak shown in Fig.2. Thiscan be seen as indicating that when balls at various speeds collide with stationary balls,
the stationary ball will be set in motion and the moving ball will stop. In this way, thegas molecules repeatedly and incessantly collide. Incidentally, regardless of how highthe average velocity is increased by raising the temperature, there will always be atleast some molecules that are going slower. At higher temperatures, naturally, themolecular velocity increases. The surface area of the graph peak represents the total
number of molecules, which remains constant. Given that the surface area is constant,when the ends of the peak spread out, the top of the peak must become lower.)(2). Glacial acetic acid:
CH3COOH, boiling point 118°C, used as a solvent for oil and resins.
(3). Benzol:
C6H6, boiling point 85°C, used to manufacture styrene and fenol.
(4). Mean free path:
For gas molecules as well as electrons within crystals, this is the average distancetraveled from one collision to the next collision.
(5). Ionic bonds:
Bonds in which positive ions and negative ions attract each other with electrostaticforce. (Example, NaCl)(6). Covalent bonds:
Bonds formed when the valence electron is shared between two separate atoms.
(Example, Cn)(7). Metallic bonds:
Bonds in which the electrons are evenly distributed between neighboring atoms, andthe metal ions form mutual attractions. This is similar to one form of ionic bond.
(Example, (Na)n)(8). Latent heat:
The amount of heat gained or lost through phase transition.
Water

water vapor 2267 kJ/kg (539.8 kcal/kg = 41 kJ/mol at 100°C)
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ice 334 kJ/Kg (79.7 cal/kg)(Reference: Why is a greater amount of heat needed to make steam than to melt ice?
The reason is that the heat to melt ice is the amount of thermal energy needed to loosen
the attraction between molecules caused by the intermolecular force within eachmolecule. The heat to vaporize water is the amount of thermal energy needed tocompletely separate the molecules. Because of this, greater energy is required tovaporize water.)(9). Hydrogen iodide (HI):
Water soluble, colorless, used as an organic synthesis reagent.

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