High School

Given the following free energies of formation:

\[ C_2H_2(g), \ \delta G_f^\circ = 209.2 \ \text{kJ/mol} \]

\[ C_2H_6(g), \ \delta G_f^\circ = -32.85 \ \text{kJ/mol} \]

Calculate \( K_p \) at 298 K for the reaction:

\[ C_2H_2(g) + 2H_2(g) \rightleftharpoons C_2H_6(g) \]

A. 97.7
B. 1.10
C. \( 8.17 \times 10^{30} \)
D. \( 2.69 \times 10^{42} \)

Answer :

The correct answer for the given chemical equation is (B) 1.10.

Equilibrium constant:

The equilibrium constant (K) is a measure of the extent to which a chemical reaction reaches equilibrium. It is defined as the ratio of the product of the concentrations of the products raised to their stoichiometric coefficients, divided by the product of the concentrations of the reactants raised to their stoichiometric coefficients, all at equilibrium.

The equilibrium constant (Kp) can be calculated using the equation:

ΔG° = -RT ln Kp

where ΔG° is the standard free energy change for the reaction, R is the gas constant (8.314 J/mol·K), T is the temperature in kelvin (298 K), and ln is the natural logarithm.

The standard free energy change for the reaction can be calculated using the free energies of formation of the reactants and products:

ΔG° = ΣnΔGf°(products) - ΣnΔGf°(reactants)

ΔG° = (1 mol)(-32.85 kJ/mol) - (1 mol)(209.2 kJ/mol) + (1 mol)(2 x 0 kJ/mol)

ΔG° = -242.9 kJ/mol

Now, substituting the values in the equation for Kp:

-ΔG° / RT = ln Kp

-(242900 J/mol) / ((8.314 J/mol·K)(298 K)) = ln Kp

ln Kp = -32.01

Kp = [tex]e^{-32.01}[/tex] = 1.10 x [tex]10^{-14}[/tex]

Therefore, the answer is (B) 1.10.

What is energy an formation?

The energy of formation (ΔHf°) is the enthalpy change that occurs when one mole of a compound is formed from its constituent elements in their standard states (i.e., the most stable form of the element at a given temperature and pressure). The standard state of an element is defined as its most stable form at 1 atmosphere pressure and a specified temperature (usually 25°C or 298 K).

The energy of formation is a thermodynamic property that provides information about the stability and reactivity of a compound. The energy of formation is usually reported in units of kilojoules per mole (kJ/mol) or kilocalories per mole (kcal/mol).

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