Skip to main content
Pearson+ LogoPearson+ Logo
Ch.18 - Free Energy and Thermodynamics
All textbooksTro 4th EditionCh.18 - Free Energy and ThermodynamicsProblem 42c
Chapter 18, Problem 42c

Given the values of ΔH°rxn, ΔS°rxn, and T, determine ΔSuniv and predict whether or not each reaction is spontaneous. (Assume that all reactants and products are in their standard states.) c. ΔH°rxn = +95 kJ; ΔS°rxn = -157 J/K; T = 298 K

Verified step by step guidance
1
First, we need to convert ΔH°rxn from kJ to J because ΔS°rxn is given in J/K. We can do this by multiplying the given ΔH°rxn by 1000. So, ΔH°rxn = +95 kJ * 1000 = +95000 J.
Next, we calculate ΔSuniv using the formula ΔSuniv = ΔS°rxn - (ΔH°rxn/T). Plug in the given values: ΔSuniv = -157 J/K - (+95000 J/298 K).
Calculate the value of ΔSuniv from the above expression.
If ΔSuniv is positive, the reaction is spontaneous. If ΔSuniv is negative, the reaction is non-spontaneous.
Finally, based on the value of ΔSuniv, predict whether the reaction is spontaneous or not.

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above.
Video duration:
5m
Was this helpful?

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Gibbs Free Energy

Gibbs Free Energy (G) is a thermodynamic potential that helps predict the spontaneity of a reaction at constant temperature and pressure. It is calculated using the equation ΔG = ΔH - TΔS, where ΔH is the change in enthalpy, T is the temperature in Kelvin, and ΔS is the change in entropy. A negative ΔG indicates a spontaneous reaction, while a positive ΔG suggests non-spontaneity.
Recommended video:
Guided course
01:51
Gibbs Free Energy of Reactions

Entropy (ΔS)

Entropy (ΔS) is a measure of the disorder or randomness in a system. In the context of a chemical reaction, a positive ΔS indicates an increase in disorder, which favors spontaneity. Conversely, a negative ΔS suggests a decrease in disorder, which can hinder spontaneity. The change in entropy is crucial for determining the overall spontaneity of a reaction when combined with enthalpy changes.
Recommended video:
Guided course
02:46
Entropy in Thermodynamics

Enthalpy (ΔH)

Enthalpy (ΔH) is a measure of the total heat content of a system and reflects the energy absorbed or released during a reaction. A positive ΔH indicates that the reaction is endothermic, absorbing heat from the surroundings, while a negative ΔH indicates an exothermic reaction, releasing heat. The sign and magnitude of ΔH are essential for evaluating the energy changes that influence the spontaneity of a reaction in conjunction with entropy.
Recommended video:
Guided course
02:34
Enthalpy of Formation
Related Practice
Textbook Question

Given the values of ΔH°rxn, ΔS°rxn, and T, determine ΔSuniv and predict whether or not each reaction is spontaneous. (Assume that all reactants and products are in their standard states.) c. ΔH°rxn = -115 kJ; ΔS°rxn = -263 J/K; T = 298 K

Textbook Question

Given the values of ΔH°rxn, ΔS°rxn, and T, determine ΔSuniv and predict whether or not each reaction is spontaneous. (Assume that all reactants and products are in their standard states.) a. ΔH°rxn = -95 kJ; ΔS°rxn = -157 J/K; T = 298 K

Textbook Question

Calculate the change in Gibbs free energy for each of the sets of ΔHrxn, ΔSrxn, and T given in Problem 42. Predict whether or not each reaction is spontaneous at the temperature indicated. (Assume that all reactants and products are in their standard states.)

Textbook Question

Calculate the free energy change for this reaction at 25 °C. Is the reaction spontaneous? (Assume that all reactants and products are in their standard states.) C3H8(g) + 5 O2(g) → 3 CO2(g) + 4 H2O(g) ΔH°rxn = -2217 kJ; ΔS°rxn = 101.1 J/K