AP Chemistry: Thermodynamics & Thermochemistry 2

Question 1

What is the sign of ΔH for an endothermic reaction?

Accepted Answer

Positive

Answer

Endothermic reactions absorb heat, so ΔH is positive.

Question 2

A 50.0 g sample of water (c = 4.18 J/g·°C) is heated from 20.0 °C to 30.0 °C. How much heat is absorbed?

Accepted Answer

2090 J

Answer

q = mcΔT = 50.0 × 4.18 × 10.0 = 2090 J.

Question 3

Which quantity is a state function?

Accepted Answer

Enthalpy

Answer

Enthalpy depends only on the state, not the path; heat and work are path-dependent.

Question 4

According to Hess's law, the enthalpy change of a reaction depends on what?

Accepted Answer

Only the initial and final states

Answer

Hess's law states ΔH depends only on initial and final states, regardless of path.

Question 5

What does a negative ΔG indicate about a process?

Accepted Answer

It is spontaneous

Answer

A negative Gibbs free energy change means the process is spontaneous.

AP Practice Test