At constant temperature and pressure, if ΔH is positive and ΔS is negative, what can be said about ΔG?
Practice Questions
1 question
Q1
At constant temperature and pressure, if ΔH is positive and ΔS is negative, what can be said about ΔG?
ΔG is positive
ΔG is negative
ΔG is zero
ΔG can be either positive or negative
If ΔH is positive and ΔS is negative, ΔG will be positive.
Questions & Step-by-step Solutions
1 item
Q
Q: At constant temperature and pressure, if ΔH is positive and ΔS is negative, what can be said about ΔG?
Solution: If ΔH is positive and ΔS is negative, ΔG will be positive.
Steps: 7
Step 1: Understand the symbols: ΔH represents enthalpy change, ΔS represents entropy change, and ΔG represents Gibbs free energy change.
Step 2: Recognize that ΔH is positive, which means the reaction absorbs heat (endothermic).
Step 3: Note that ΔS is negative, indicating that the disorder of the system decreases.
Step 4: Recall the Gibbs free energy equation: ΔG = ΔH - TΔS, where T is the temperature in Kelvin.
Step 5: Since ΔH is positive and ΔS is negative, the term -TΔS will also be negative (because a negative ΔS multiplied by a positive temperature is negative).
Step 6: Therefore, when you combine a positive ΔH and a negative -TΔS, the overall ΔG will be positive.
Step 7: Conclude that if ΔH is positive and ΔS is negative, then ΔG is positive, indicating that the reaction is non-spontaneous under these conditions.
