Question

(I already have part A but still still include it anyways so you can use its data to solve for parts B and C.

Chemical energy is released or absorbed from reactions in various forms. The most easily measurable form of energy comes in the form of heat, or enthalpy. The enthalpy of a reaction can be calculated from the heats of formation of the substances involved in the reaction:

ΔH∘rxn=ΔH∘f(products)−ΔH∘f(reactants)

Entropy change, ΔS∘, is a measure of the number of energetically equivalent microstates introduced into the system during the reaction. The degree of spontaneity of a reaction is represented by the Gibbs free energy, ΔG∘. The Gibbs free energy depends on both the enthalpy and entropy changes that take place during the reaction:

ΔG∘=ΔH∘−TΔS∘

where T is standard temperature, 298 K.

Part A

Part complete

Calculate the standard enthalpy change for the reaction

2A+B⇌2C+2D

where the heats of formation are given in the following table:

Substance	ΔH∘f (kJ/mol)
A	-261
B	-425
C	175
D	-491

Express your answer in kilojoules.

ΔH∘rxn = 315 kJ  

Part B

For the reaction given in Part A, how much heat is absorbed when 3.30 mol of A reacts?

Express your answer numerically in kilojoules.

Part C

For the reaction given in Part A, ΔS∘rxn is 41.0 J/K . What is the standard Gibbs free energy of the reaction, ΔG∘rxn?

Express your answer numerically in kilojoules.

Answer 1

Part A
The given reaction is

Hence, the standard enthalpy change of the reaction can be calculated as follows:

Hence, the standard enthalpy change of the reaction is 315 kJ.

Part B

When 2 moles of A reacts, 315 kJ of heat s absorbed.

Note that the coefficient of A is 2 in the reaction.

Hence, amount of heat absorbed when 3.30 mol of A reacts can be calculated as

Hence, the amount of heat absorbed is 520 kJ. (Rounded to three significant figures).

Part C

Given that

T = 298 K

We can calculate the standard Gibbs free energy change as follows:

Hence, the standard Gibbs free energy of the reaction is about 303 kJ. (Rounded to three significant figures)