APCE Thermodynamics & Thermochemistry

Question 1

What does the first law of thermodynamics state?

Accepted Answer

Energy is conserved in all processes.

Answer

Energy can be created and destroyed.

Answer

Energy is lost as heat.

Answer

Energy can only be transferred by work.

Question 2

What is enthalpy (ΔH)?

Accepted Answer

The heat content of a system.

Answer

The total energy of the system.

Answer

The change in pressure.

Answer

The energy released during a chemical reaction.

Question 3

What is the difference between exothermic and endothermic reactions?

Accepted Answer

Exothermic reactions release heat, and endothermic reactions absorb heat.

Answer

Exothermic reactions absorb heat, and endothermic reactions release heat.

Answer

Both reactions release heat.

Answer

Both reactions absorb heat.

Question 4

What is Gibbs free energy (ΔG)?

Accepted Answer

The energy available to do work at constant temperature and pressure.

Answer

The total heat energy of a system.

Answer

The change in pressure of a system.

Answer

The energy released during an exothermic reaction.

Question 5

What is the standard enthalpy of formation (ΔHf°)?

Accepted Answer

The heat change when one mole of a compound is formed from its elements in their standard states.

Answer

The heat released when a substance is burned.

Answer

The heat required to break a bond.

Answer

The heat released during a chemical reaction.

Question 6

What is the second law of thermodynamics?

Accepted Answer

Entropy of an isolated system increases over time.

Answer

The total energy of the universe is constant.

Answer

Entropy of an isolated system decreases over time.

Answer

Energy cannot be transferred as heat.

Question 7

What is the relationship between temperature and entropy?

Accepted Answer

As temperature increases, entropy increases.

Answer

As temperature increases, entropy decreases.

Answer

As temperature decreases, entropy increases.

Answer

Temperature has no effect on entropy.

Question 8

What is the relationship between enthalpy change (ΔH) and heat in a reaction?

Accepted Answer

Enthalpy change represents the heat released or absorbed at constant pressure.

Answer

Enthalpy change is unrelated to heat.

Answer

Enthalpy change is the energy required to break bonds.

Answer

Enthalpy change represents the temperature change in a reaction.

Question 9

What is the heat of reaction?

Accepted Answer

The heat absorbed or released during a reaction, represented as ΔH.

Answer

The total heat content of reactants.

Answer

The energy required to break bonds.

Answer

The energy required to form products.