Chemistry Test Thermochemistry 3

Question 1

Which statement correctly describes entropy (S)?

Accepted Answer

Entropy is a measure of disorder or dispersal of energy

Answer

Entropy quantifies the number of microstates available to a system, reflecting disorder or energy dispersal.

Question 2

For a spontaneous process at constant temperature and pressure, the Gibbs free energy change (ΔG) must be:

Accepted Answer

Negative

Answer

A negative ΔG indicates a spontaneous process; ΔG < 0 means the reaction releases free energy.

Question 3

The relationship ΔG = ΔH − TΔS shows that a reaction is spontaneous at all temperatures when:

Accepted Answer

ΔH < 0 and ΔS > 0

Answer

When ΔH is negative and ΔS is positive, ΔG is negative regardless of temperature.

Question 4

The heat of solution of NH₄NO₃ in water is endothermic (+25.7 kJ/mol). This means dissolving NH₄NO₃:

Accepted Answer

Cools the solution

Answer

An endothermic dissolution absorbs heat from the solution, lowering the temperature.

Question 5

What is the standard enthalpy change (ΔH°rxn) calculated from bond energies if bonds broken require 800 kJ and bonds formed release 950 kJ?

Accepted Answer

-150 kJ

Answer

ΔH°rxn = energy in (bonds broken) − energy out (bonds formed) = 800 − 950 = −150 kJ.

Chemistry Practice Test