A decomposition reaction is when a more complex substance breaks down into its more simple parts. It is thus the opposite of a synthesis reaction, and can be written as:
One example of a decomposition reaction is the electrolysis of water to make oxygen and hydrogen gas:
Another example of a decomposition reaction is calcium carbonate breaking down into calcium oxide and carbon dioxide under high temperatures:
CaCO —> CaO + CO
In a single replacement reaction, a single uncombined element replaces another in a compound; in other words, one element trades places with another element in a compound These reactions come in the general form of:
One example of a single displacement reaction is when magnesium replaces hydrogen in water to make magnesium hydroxide and hydrogen gas:
In a double replacement reaction, the anions and cations of two compounds switch places and form two entirely different compounds. These reactions are in the general form:
For example, when barium chloride (BaCl) and magnesium sulfate (MgSO) react, the SO anion switches places with the 2Cl anion, giving the compounds BaSO and MgCl.
Another example of a double displacement reaction is the reaction of lead(II) nitrate with potassium iodide to form lead(II) iodide and potassium nitrate:
A chemical reaction is being displayed by an equation:
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Rectangle
In geometry, a rectangle is a shape with four sides and four corners. The corners are all right angles. It follows that the pairs of sides opposite each other must be parallel and of the same length.
People make many rectangular things, including most tables, boxes, books, and papers. The word comes from Latin words meaning "right" and angle".
A rectangle whose four sides have the same length is called a square.
If a rectangle has length formula_1 and width "w", then":"
Trafalgar Square
Trafalgar Square is in the heart of London. It is a large pedestrian square, bounded on three sides by roads. It serves as a refuge, and a major traffic intersection. Important roads go from the square: Whitehall goes to Parliament, the Mall goes to Buckingham Palace, and the Strand goes to the City of London. The square is also close to Covent Garden and Charing Cross station.
More than 15 million people go to visit there every year. It contains a large statue of Admiral Lord Nelson. The square celebrates the Battle of Trafalgar, fought in 1805. It contains Nelson's Column, a statue of Nelson mounted on a tall column, with four statues of lions around it. The column is 56 meters tall while the statue is 5 meters tall. The National Art Gallery is one of several important buildings facing the square.
The square is visited by many tourists. Mainly, it is used for pleasure and relaxation, but sometimes there are meetings and demonstrations in Trafalgar Square.
When the square was first built, demonstrations were banned. The ban lasted until the 1880s, when the new Labour movement start to hold demonstrations. One group that did this was the Social Democratic Federation. On "Black Monday", 6 February 1886, there was a major demonstration about unemployment which led to a riot in Pall Mall. There were demonstrations in the 1980s against South African apartheid. In 1990 there were riots against the Poll tax. In the 2000s there have been demonstrations against the Iraq war.
In recent years the square has become a gathering place for celebrations. When England won the Rugby World Cup in 2003 thousands of fans gathered in the square. This public festivities again happened when London won its bid to hold the 2012 Summer Olympic Games.
The square was also the scene of a large gathering after the terrorist bombings in London on 7 July 2005.
Official language
An official language is a language that has special status in a country or other organization. Usually, the government does its business in the official language. They are sometimes named in a country's constitution.
Some countries, like Switzerland and Luxembourg, have more than one official language. Other countries, such as the United States and Australia, may not have a "de jure" official language set by law, but they may have one or more national languages that is considered "de facto" official because it is used by the government and people in the country.
An official language does not have to be a written language. It can be a pidgin language (like in Papua New Guinea), or a sign language (like in New Zealand).
Cake
A cake is a type of (usually) sweet dessert which is baked. Originally, it was a bread-like food, but no longer. Cakes are often made to celebrate special occasions like birthdays or weddings. There are many kinds of cakes. It can be baked in an oven. Some savory cakes are made on a griddle or a frying pan.
Cakes are baked from a batter. Batter is made by mixing wet ingredients (like milk and eggs) with dry ingredients (like sugar and flour). The batter is baked in an oven. This way of baking is known as the muffin method, because muffins are made this way.
Just like bread, cakes rise in the oven because they contain many small air bubbles. As cakes rise, the air bubbles expand. This is why the cake batter expands in the pan (often to twice its original size). There are two ways of forming the air bubbles, which create different types of cakes. Almost every kind of cake belongs to one of these families.
These cakes are made with butter or another fat, like vegetable shortening. The common way is to mix the fat and sugar, then add eggs, and then add flour. The fat should be soft. It should not be hard or liquid. Mixing sugar with fat creates many very small air bubbles. Most birthday cakes are made this way. Cupcakes are also made this way.
These cakes are not made with solid butter or vegetable shortening. Some of these cakes are made with melted butter or vegetable oil. The common way is to mix the eggs and sugar, and then add flour. These cakes are often much taller, lighter and often spongier than creamed fat cakes. Angelfood cake and chiffon cakes are egg foam cakes. Most grocery stores with bakeries sell angelfood cakes. Angelfood cakes are made by beating egg whites with sugar. This traps a lot of tiny air bubbles. The eggs and sugar are mixed with other ingredients. Then, the cake is baked.
A cake can be decorated with icing (also called "frosting"), chocolate, fruit, and much more. A layer cake is made by stacking cakes with icing or filling between the layers. Birthday cakes are sometimes decorated with candles. Cakes can be served with berries or other kinds of fruit.
A large, rich cake is often called by the French word for "cake": "gâteau" (plural: "gâteaux", both singular and plural pronounced "GA-toe"). It may have a lot of cream. Some cakes can have edible paper on the top.
House
A house is a building that is made for people to live in. It is a "permanent" building that is meant to stay standing. It is not easily packed up and carried away like a tent, or moved like a caravan. If people live in the same house for more than a short stay, then they call it their "home". Being without a home is called homelessness.
Houses come in many different shapes and sizes. They may be as small as just one room, or they may have hundreds of rooms. They also are made many different shapes, and may have just one level or several different levels. A house is sometimes joined to other houses at the sides to make a "terrace" or "row house" (a connected row of houses).
A big building with many levels and apartments is called "a block of flats" (British) or an apartment building. One of the differences between a house and an apartment is that a house has a front door to the outside world, whereas the main door of an apartment usually opens onto a passage or landing that can be used by other people in the building.