NEET Thermodynamics — Set 19

Question 1

Which of the following is a state function?

Accepted Answer

A state function depends only on the initial and final states, not the path taken. Internal energy ($U$) is a state function, while work ($w$) and heat ($q$) are path-dependent.

Question 2

The enthalpy of combustion of benzene is -3267.6 kJ/mol. What is the heat released when 39 g of benzene is burnt? (Molar mass = 78 g/mol)

Accepted Answer

Moles = $39 / 78 = 0.5 \, \text{mol}$, heat released = $0.5 \times 3267.6 = 1633.8 \, \text{kJ}$.

Question 3

Calculate $ \Delta S_{sys} $ when 2 mol of an ideal gas expands isothermally from 1 atm to 0.25 atm at 300 K. ($ R = 8.314 \, \text{J/mol·K} $)

Accepted Answer

For isothermal expansion, $ \Delta S_{sys} = nR \ln(P_1/P_2) = 2 \times 8.314 \times \ln(1/0.25) = 16.628 \times 1.3863 \approx 23.0 \, \text{J/K} $.

NEET Chemistry: Thermodynamics — Practice Set 19

Q1. Which of the following is a state function?

Q2. The enthalpy of combustion of benzene is -3267.6 kJ/mol. What is the heat released when 39 g of benzene is burnt? (Molar mass = 78 g/mol)

Q3. Calculate \( \Delta S_{sys} \) when 2 mol of an ideal gas expands isothermally from 1 atm to 0.25 atm at 300 K. (\( R = 8.314 \, \text{J/mol·K} \))

Q4. Calculate \(\Delta S_{sys}\) when 1 mol of an ideal gas expands isothermally from 4 L to 16 L at 500 K. (\(R = 8.314 \, \text{J/mol·K}\))

Q5. Which of the following is always true for an exothermic process at constant pressure?

Q6. Calculate \(\Delta H\) for \(C(s) + CO_2(g) \rightarrow 2CO(g)\) using: \(C(s) + O_2(g) \rightarrow CO_2(g)\), \(\Delta H = -393.5 \, \text{kJ/mol}\); \(CO(g) + \frac{1}{2}O_2(g) \rightarrow CO_2(g)\), \(\Delta H = -283 \, \text{kJ/mol}\).

Q7. Calculate the bond enthalpy of \( C=O \) in \( CO(g) \) given: \( \Delta H_f^\circ (CO,g) = -110.5 \, \text{kJ/mol} \), \( \Delta H_a (C,g) = 715.0 \, \text{kJ/mol} \), \( \Delta H_a (O,g) = 249.0 \, \text{kJ/mol} \).

Q8. For a reaction with \(\Delta H = 90 \, \text{kJ/mol}\) and \(\Delta G = 30 \, \text{kJ/mol}\) at 300 K, what is \(\Delta S\)?

Q10. Calculate \(\Delta S_{sys}\) when 1 mol of an ideal gas is compressed isothermally from 25 L to 5 L at 350 K. (\(R = 8.314 \, \text{J/mol·K}\))