For the reaction: 2SO2(g) + O2(g) = 2SO3(g) conducted at 25°C and 1 atm.
Calculate H°, S°, G°
To calculate the standard enthalpy change (ΔH°), standard entropy change (ΔS°), and standard free energy change (ΔG°) for the given reaction, we need to look up the values for the standard enthalpy of formation (ΔH°f) and standard entropy (ΔS°) for each compound involved.
The standard enthalpy change (ΔH°) is calculated using the following equation:
ΔH° = Σ(n ΔH°f,products) - Σ(n ΔH°f,reactants)
Where:
n = coefficients in the balanced equation
ΔH°f = standard enthalpy of formation
The standard entropy change (ΔS°) is calculated using the following equation:
ΔS° = Σ(n ΔS°,products) - Σ(n ΔS°,reactants)
Where:
n = coefficients in the balanced equation
ΔS° = standard entropy
The standard free energy change (ΔG°) is calculated using the following equation:
ΔG° = ΔH° - TΔS°
Where:
ΔH° = standard enthalpy change
ΔS° = standard entropy change
T = temperature in Kelvin (25°C = 298 K)
Let's calculate the values step-by-step:
Step 1: Find the standard enthalpy of formation (ΔH°f) and standard entropy (ΔS°) values for each compound involved:
ΔH°f (SO2) = -296.83 kJ/mol
ΔH°f (O2) = 0 kJ/mol
ΔH°f (SO3) = -395.72 kJ/mol
ΔS° (SO2) = 248.18 J/(mol·K)
ΔS° (O2) = 205.14 J/(mol·K)
ΔS° (SO3) = 256.27 J/(mol·K)
Step 2: Calculate ΔH°:
ΔH° = (2 ΔH°f (SO3)) - (2 ΔH°f (SO2) + ΔH°f (O2))
= (2 * (-395.72 kJ/mol)) - (2 * (-296.83 kJ/mol) + 0 kJ/mol)
= -148.98 kJ/mol
Step 3: Calculate ΔS°:
ΔS° = (2 ΔS° (SO3)) - (2 ΔS° (SO2) + ΔS° (O2))
= (2 * 256.27 J/(mol·K)) - (2 * 248.18 J/(mol·K) + 205.14 J/(mol·K))
= 310.04 J/(mol·K)
Step 4: Calculate ΔG°:
ΔG° = ΔH° - TΔS°
= -148.98 kJ/mol - (298 K * (310.04 J/(mol·K) / 1000))
= -148.98 kJ/mol - 91.727 kJ/mol
= -240.707 kJ/mol
Therefore, the values for H°, S°, and G° for the reaction are:
ΔH° = -148.98 kJ/mol
ΔS° = 310.04 J/(mol·K)
ΔG° = -240.707 kJ/mol
To calculate the standard enthalpy change (ΔH°), standard entropy change (ΔS°), and standard Gibbs free energy change (ΔG°) for the given reaction, you will need the standard enthalpy of formation (ΔH°f) and standard entropy (S°) data for the reactants and products involved.
1. Find the standard enthalpy change (ΔH°):
The standard enthalpy change (ΔH°) can be calculated using the standard enthalpy of formation (ΔH°f) values for the reactants and products. The equation is given by:
ΔH° = Σ(ΔH°f, products) - Σ(ΔH°f, reactants)
Look up the standard enthalpy of formation (ΔH°f) values for SO2(g), O2(g), and SO3(g) from a reference source (such as a chemistry textbook or online database).
Assume the standard enthalpy of formation (ΔH°f) of SO2(g) = 0, as it is often used as a reference point in thermochemistry.
2. Find the standard entropy change (ΔS°):
The standard entropy change (ΔS°) can be calculated using the standard entropy (S°) values for the reactants and products. The equation is given by:
ΔS° = Σ(S°, products) - Σ(S°, reactants)
Look up the standard entropy (S°) values for SO2(g), O2(g), and SO3(g) from a reference source, such as a chemistry textbook or online database.
3. Find the standard Gibbs free energy change (ΔG°):
The standard Gibbs free energy change (ΔG°) can be calculated using the equation:
ΔG° = ΔH° - TΔS°
where T is the temperature in Kelvin (25°C = 298 K).
Plug in the values of ΔH° and ΔS° obtained in steps 1 and 2 to calculate ΔG°.
Remember to ensure that the units for all values are consistent (e.g., kJ/mol, J/K, etc.) before calculation.
dHrxn = (n*dHformation products) - (n*dHformation reactants)
dSrxn = (n*dSformation products) - (n*dSformation reactants)
Then dGrxn = dHrxn - TdSrxn