For a particular reaction, ΔH = -328.21 kJ and ΔS = 98.7 J/K. Calculate ΔG for this reaction at 298 K.
To calculate ΔG (Gibbs free energy) for the reaction, we can use the equation:
ΔG = ΔH - TΔS
where:
ΔH = enthalpy change
ΔS = entropy change
T = temperature in Kelvin
Given:
ΔH = -328.21 kJ
ΔS = 98.7 J/K
T = 298 K
First, convert ΔH to the same unit as ΔS (J) by multiplying by 1000 since 1 kJ = 1000 J:
ΔH = -328.21 kJ x 1000 J/kJ = -328210 J
Now, we can substitute the values into the equation:
ΔG = ΔH - TΔS
= -328210 J - (298 K)(98.7 J/K)
= -328210 J - 29487 J
= -357697 J
So, the ΔG for the reaction at 298 K is -357697 J.
To calculate ΔG (Gibbs free energy) for a reaction, we can use the following equation:
ΔG = ΔH - TΔS
Where:
ΔH = Enthalpy change (in kJ)
ΔS = Entropy change (in J/K)
T = Temperature (in K)
In this case, ΔH = -328.21 kJ, ΔS = 98.7 J/K, and T = 298 K.
Step 1: Convert ΔH to kJ (from J):
ΔH = -328.21 kJ
Step 2: Convert ΔS to kJ/K (from J/K):
ΔS = 98.7 J/K = 0.0987 kJ/K
Step 3: Calculate ΔG using the equation:
ΔG = ΔH - TΔS
ΔG = -328.21 kJ - (298 K × 0.0987 kJ/K)
ΔG = -328.21 kJ - 29.6806 kJ
Step 4: Perform the subtraction to find the value of ΔG:
ΔG = -357.8906 kJ
Therefore, the value of ΔG for this reaction at 298 K is approximately -357.8906 kJ.
dG = dH - TdS
The mistake most students make is that they don't change dS to kJ before the calculation.