Problem: Robert, a baker, has just baked a large batch of cupcakes for his store. He won't be able to sell all of his cupcakes within the next week, so he has decided to store a portion of them in the freezer to preserve them for later. He is trying to decide if he should store the cupcakes at 0 F or at 10 F in the freezer. Which temperature will result in slower decay of the cupcakes? Hint: Freezing is a common method of food preservation that slows both food decay and the growth of micro-organisms. Besides the effect of lower temperatures on reaction rates, freezing makes water less available for bacterial growth.

A: 0 F

Problem: Two villages experienced flooding this spring. Berg village used many sandbags to protect from the dam overflowing. Creek village didn't use any sandbags, they were caught by surprise. Which village was more affected by the dam overflowing? Hint: People protect areas that might flood with dams. In dire situations, they use sandbags ( Figure below ). Dams are usually very effective, but high water levels sometimes cause a dam to break. In that case, flooding can be catastrophic. Flood waters can also overflow a dam. People may line a river bank with levees to protect against floods. These are high walls that keep the stream within its banks during floods. Flood protection in one location sometimes causes problems elsewhere. For example, a levee in one location may just force the high water upstream or downstream. This will lead to flooding in a different location. Sometimes water gets so high that the river must be allowed to flood.

A: Creek

Problem: A scientist is in the lab testing mixing water with different chemicals. While working with chemical A he notes that the water becomes colder after combining them. With chemical B the water becomes much warmer. Given the changes in temperature, does chemical A cause an exothermic process or an endothermic process? Hint: Some materials have negative heats of solution; the dissolution of one of these solutes in water is an exothermic process. Heat is released, causing a net increase in the temperature of the solution. Conversely, other substances have positive heats of solution. For example, the dissolution of potassium nitrate in water is an endothermic process. The resulting absorption of energy causes the solution to become colder. Calculations involving heats of solutions follow the same basic approach that we have used with other enthalpy problems.

A: exothermic

Problem: Rob is testing the properties of gas. To that end, he experimented with a cylinder of gas in three stages, stage A, stage B, and stage C. In stage A he kept the gas in room temperature. In stage B he heated the gas up. And in stage C he cooled the gas down. Which stage would see increased pressure, stage B or stage C? Hint: Shown in the Figure below is a cylinder of gas on the left that is at room temperature (300 K). On the right, the cylinder has been heated until the Kelvin temperature has doubled to 600 K. The kinetic energy of the gas molecules increases, so collisions with the walls of the container are now more forceful than they were before. As a result, the pressure of the gas doubles. Decreasing the temperature would have the opposite effect, and the pressure of an enclosed gas would decrease.

A:
stage B