Methanol (CH3OH) is made industrially in two steps from CO and H2. It is so cheap to make that it is being considered for use as a precursor to hydrocarbon fuels, such as methane (CH4): Step 1. CO(g) + 2 H2(g) ⇌ CH3OH(l) ΔS° = -332 J/K Step 2. CH3OH(l) ⇌ CH4(g) + 1/2 O2(g) ΔS° = 162 J/K. (g) Calculate ΔG° for step 2. (d) Which term is more important, ΔH° or ΔS°? (i) Which term is more important, ΔH° or ΔS°?

Verified step by step guidance

1. To calculate ΔG° for step 2, use the Gibbs free energy equation: ΔG° = ΔH° - TΔS°. You will need the values of ΔH° and ΔS° for step 2, as well as the temperature T in Kelvin.
2. Since ΔS° for step 2 is given as 162 J/K, ensure that the units are consistent when using the Gibbs free energy equation. If ΔH° is in kJ, convert ΔS° to kJ by dividing by 1000.
3. Determine the temperature T at which you want to calculate ΔG°. If not specified, standard conditions (298 K) are often used.
4. Substitute the values of ΔH°, T, and ΔS° into the Gibbs free energy equation to find ΔG° for step 2.
5. To determine which term is more important, ΔH° or ΔS°, consider the magnitude of each term in the Gibbs free energy equation. Compare the absolute values of TΔS° and ΔH° to see which has a greater impact on ΔG°.

Key Concepts

Gibbs Free Energy (ΔG°)

Gibbs Free Energy (ΔG°) is a thermodynamic potential that measures the maximum reversible work obtainable from a thermodynamic system at constant temperature and pressure. It is calculated using the equation ΔG° = ΔH° - TΔS°, where ΔH° is the change in enthalpy and ΔS° is the change in entropy. A negative ΔG° indicates that a reaction is spontaneous under standard conditions, while a positive ΔG° suggests non-spontaneity.

Enthalpy (ΔH°)

Enthalpy (ΔH°) is a measure of the total heat content of a system, reflecting the energy required to create a system at constant pressure. It accounts for both internal energy and the energy associated with pressure and volume. In chemical reactions, a negative ΔH° indicates an exothermic reaction, where heat is released, while a positive ΔH° indicates an endothermic reaction, where heat is absorbed.

Entropy (ΔS°)

Entropy (ΔS°) is a measure of the disorder or randomness in a system. It quantifies the number of ways a system can be arranged, with higher entropy indicating greater disorder. In chemical reactions, an increase in entropy (positive ΔS°) often favors spontaneity, as systems tend to evolve towards states of higher disorder. The relationship between ΔS° and spontaneity is crucial in determining the overall feasibility of a reaction.