Chapter 6/17 Thermodynamics MCQ Assessment

Front

What is the standard entropy change (ΔS°) for a reaction?

Back

The standard entropy change (ΔS°) for a reaction is calculated using the formula: ΔS° = ΣS°(products) - ΣS°(reactants). It indicates the change in disorder or randomness in a system.

Front

How do you calculate the standard entropy change for the reaction: 2Cu(s) + O2(g) → 2CuO(s)?

Back

ΔS° = [2 * S°(CuO)] - [2 * S°(Cu) + S°(O2)] = [2 * 42.5] - [2 * 33.15 + 205.14] = -93.22 J/K·mol.

Front

What drives spontaneous reactions?

Back

Spontaneous reactions are driven by decreasing enthalpy (ΔH) and increasing entropy (ΔS).

Front

What is Gibbs free energy (ΔG) and how is it calculated?

Back

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 formula: ΔG = ΔH - TΔS.

Front

Calculate ΔG° at 298 K for the combustion of methane: CH4(g) + 2 O2(g) → CO2(g) + 2 H2O(g).

Back

ΔG° = [ΔG°(CO2) + 2 * ΔG°(H2O)] - [ΔG°(CH4) + 2 * ΔG°(O2)] = [-394.4 + 2 * (-228.57)] - [-50.8 + 0] = -801 kJ.

Front

What is specific heat capacity?

Back

Specific heat capacity is the amount of heat required to raise the temperature of one gram of a substance by one degree Celsius (°C).

Front

How much heat does an aluminum block absorb if 10.00 grams are heated from 25.0°C to 50.0°C?

Back

Heat absorbed (q) = mass * specific heat * change in temperature = 10.00 g * 0.900 J/g°C * (50.0 - 25.0)°C = 225 J.

Front

What are the signs of ΔH, ΔS, and ΔG for the reaction: Mg(s) → Mg(g)?

Back

ΔH = + (endothermic), ΔS = + (increase in disorder), ΔG = - (spontaneous at high temperatures).

Front

Define enthalpy (ΔH).

Back

Enthalpy (ΔH) is a measure of the total heat content of a system, reflecting the internal energy plus the product of pressure and volume.

Front

What is entropy (S)?

Back

Entropy (S) is a measure of the disorder or randomness in a system, indicating the number of ways a system can be arranged.