1.
How much heat energy must be absorbed to completely melt 35.0 grams of H2O(s) at STP?
Correct Answer
C. 11 700 J
Explanation
To completely melt 35.0 grams of H2O(s) at STP, we need to calculate the heat energy required using the equation Q = m × ΔHf, where Q is the heat energy, m is the mass of the substance, and ΔHf is the heat of fusion. The heat of fusion for water is 334 J/g. By substituting the values into the equation, we get Q = 35.0 g × 334 J/g = 11,690 J. Rounding to the nearest whole number, the correct answer is 11 700 J.
2.
The temperature of a sample of water changes from 10C to 20C when the water absorbs 418 joules of heat. What is the mass of the sample?
Correct Answer
B. 10 g
Explanation
The temperature change of a substance is directly proportional to the amount of heat absorbed. In this case, the water's temperature increased by 10 degrees Celsius when it absorbed 418 joules of heat. This indicates that the specific heat capacity of water is 41.8 J/g°C. To find the mass of the sample, we can use the formula Q = mcΔT, where Q is the heat absorbed, m is the mass, c is the specific heat capacity, and ΔT is the temperature change. Rearranging the formula to solve for mass, we get m = Q / (cΔT). Substituting the given values, we find that the mass of the sample is 10 g.
3.
What is the total number of joules released when a 5.00-gram sample of water changes from liquid to solid at STP?
Correct Answer
B. 1670 J
Explanation
When a substance changes from one state to another, such as from liquid to solid, energy is either released or absorbed. In this case, the water is changing from liquid to solid, which is an exothermic process. This means that energy is released in the form of heat. The amount of energy released is known as the heat of fusion, which for water is approximately 334 J/g. Since the sample size is given as 5.00 grams, we can calculate the total energy released by multiplying the heat of fusion by the mass of the sample: 334 J/g * 5.00 g = 1670 J. Therefore, the correct answer is 1670 J.
4.
Which sample of Fe contains particles having the highest average kinetic energy?
Correct Answer
C. 5 g at 400 K
Explanation
The average kinetic energy of particles is directly proportional to their temperature. In this case, the sample with the highest average kinetic energy would be the one with the highest temperature. Therefore, the sample of Fe that contains particles having the highest average kinetic energy is the 5 g at 400 K.
5.
The heat of fusion for a substance is 122 joules per gram. How many joules of heat are needed to melt 7.50 grams of this substance at its melting point?
Correct Answer
915
915J
915 J
Explanation
The heat of fusion for a substance is the amount of heat energy required to change a substance from a solid to a liquid at its melting point. In this question, the heat of fusion is given as 122 joules per gram. To find the total amount of heat energy needed to melt 7.50 grams of the substance, we can multiply the heat of fusion by the mass. Therefore, 122 joules/gram x 7.50 grams = 915 joules.
6.
An increase in the average kinetic energy of a sample of copper atoms occurs with an increase in:
Correct Answer
B. Temperature
Explanation
An increase in the average kinetic energy of a sample of copper atoms occurs with an increase in temperature. Temperature is a measure of the average kinetic energy of particles in a substance. As the temperature increases, the particles gain more energy and move faster, resulting in an increase in their average kinetic energy. This is true for copper atoms as well. Concentration, pressure, and volume do not directly affect the average kinetic energy of copper atoms.
7.
At which temperature would atoms of a He(g) sample have the greatest average kinetic energy?
Correct Answer
B. 37 C
Explanation
At higher temperatures, the average kinetic energy of particles increases. Since the options are given in both Celsius and Kelvin, we can convert 37°C to Kelvin by adding 273 to it, giving us 310 K. Comparing the given options, 310 K is the highest temperature listed. Therefore, atoms of a He(g) sample would have the greatest average kinetic energy at 37°C.
8.
As the temperature of a substance decreases, the average kinetic energy of its particles.
Correct Answer
A. Decreases
Explanation
As the temperature of a substance decreases, the average kinetic energy of its particles decreases. This is because temperature is directly related to the average kinetic energy of particles. When the temperature decreases, the particles have less energy and move more slowly. Therefore, the average kinetic energy decreases.