NEET Thermodynamics — Set 15

Question 1

Calculate the heat required to raise the temperature of 27 g of Al from 25°C to 45°C. (Molar heat capacity of Al = 24 J/mol·K, molar mass = 27 g/mol)

Accepted Answer

Moles = $27 / 27 = 1 \, \text{mol}$, $\Delta T = 20 \, \text{K}$, $q = nC_p\Delta T = 1 \times 24 \times 20 = 480 \, \text{J} = 0.48 \, \text{kJ}$.

Question 2

For the reaction $ 2H_2S(g) + 3O_2(g) \rightarrow 2H_2O(l) + 2SO_2(g) $, $ \Delta n_g = -3 $. If $ \Delta H = -1124.00 \, \text{kJ/mol} $ at 298 K, what is $ \Delta U $? ($ R = 8.314 \, \text{J/mol·K} $)

Accepted Answer

$ RT = 8.314 \times 298 \times 10^{-3} = 2.4776 \, \text{kJ/mol} $. Using $ \Delta H = \Delta U + \Delta n_g RT $, $ \Delta U = -1124.00 - (-3 \times 2.4776) = -1124.00 + 7.4328 = -1116.57 \, \text{kJ/mol} $.

Question 3

For the reaction $ H_2(g) + \frac{1}{2}O_2(g) \rightarrow H_2O(l) $, $ \Delta H = -286.00 \, \text{kJ/mol} $. If $ \Delta n_g = -1.5 $, what is $ \Delta U $ at 298 K? ($ R = 8.314 \, \text{J/mol·K} $)

Accepted Answer

For $ \Delta n_g = -1.5 $, $ RT = 8.314 \times 298 \times 10^{-3} = 2.4776 \, \text{kJ} $. Using $ \Delta H = \Delta U + \Delta n_g RT $, $ \Delta U = -286.00 - (-1.5 \times 2.4776) = -286.00 + 3.7164 = -282.28 \, \text{kJ/mol} $.

NEET Chemistry: Thermodynamics — Practice Set 15

Q1. Calculate the heat required to raise the temperature of 27 g of Al from 25°C to 45°C. (Molar heat capacity of Al = 24 J/mol·K, molar mass = 27 g/mol)

Q2. For the reaction \( 2H_2S(g) + 3O_2(g) \rightarrow 2H_2O(l) + 2SO_2(g) \), \( \Delta n_g = -3 \). If \( \Delta H = -1124.00 \, \text{kJ/mol} \) at 298 K, what is \( \Delta U \)? (\( R = 8.314 \, \text{J/mol·K} \))

Q3. For the reaction \( H_2(g) + \frac{1}{2}O_2(g) \rightarrow H_2O(l) \), \( \Delta H = -286.00 \, \text{kJ/mol} \). If \( \Delta n_g = -1.5 \), what is \( \Delta U \) at 298 K? (\( R = 8.314 \, \text{J/mol·K} \))

Q5. A system absorbs 800 J of heat at constant volume, and its temperature rises by 10 K. If \(C_v = 20 \, \text{J/mol·K}\), how many moles are present?

Q6. Calculate the entropy change (\(\Delta S\)) when 1 mol of an ideal gas is compressed isothermally from 20 L to 5 L at 400 K. (\(R = 8.314 \, \text{J/mol·K}\))

Q7. Calculate \(\Delta H\) for \(2C(s) + O_2(g) \rightarrow 2CO(g)\) given: \(C(s) + O_2(g) \rightarrow CO_2(g)\), \(\Delta H = -393.5 \, \text{kJ/mol}\); \(2CO(g) + O_2(g) \rightarrow 2CO_2(g)\), \(\Delta H = -566 \, \text{kJ/mol}\).

Q8. For an ideal gas undergoing reversible adiabatic expansion, which quantity remains constant?

Q9. Calculate \(\Delta S_{total}\) when 1 mol of a liquid vaporizes at 400 K if \(\Delta H_{vap} = 35 \, \text{kJ/mol}\).

Q10. The standard enthalpy of formation of \(SO_3(g)\) is -395.7 kJ/mol. What is \(\Delta H\) for \(2SO_2(g) + O_2(g) \rightarrow 2SO_3(g)\) if \(\Delta H_f^\circ (SO_2,g) = -296.8 \, \text{kJ/mol}\)?