Kf vs Kp: Examining Equilibrium Constant Dependence on Temperature & Pressure

In summary, the Kf (thermodynamic equilibrium constant) is exact and not dependent on temperature, while Kp (apparent equilibrium constant) is dependent on temperature. They are essentially the same formula, except for an activity coefficient which does not change with temperature. Kf is also dependent on pressure, but the activity coefficient compensates for this change. The equilibrium constant is dependent on temperature according to the van't Hoff equation, where \Delta H is the enthalpy of reaction.
  • #1
zmike
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Why is that the Kf (thermodynamic equilibrium constant) exact and not dependent on temperature meanwhile Kp (apparent equilibrium constant) is dependent on temperature.
They are essentially the same formula except for an activity coefficient which doesn't change in response to temperature??

also does Kf (thermodynamic equilibrium constant) is independent or dependent of pressure because

I know Kp (apparent equilibrium constant) is dependent on pressure. Does Kf depend on the partial pressure of the gases in a mixture? if so, is it the activity coefficient that compensates for this change (a different coefficient for each mixture of pressures)?

thank you
 
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  • #2
well, the equilibrium constant is dependent on temperature according to van't Hoff equation

[tex]\ln(\frac{K_2}{K_1})=\frac{\Delta H}{R}\left({1\over T_1}-{1\over T_2}\right)[/tex]

where \Delta H is the enthalpy of reaction
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Related to Kf vs Kp: Examining Equilibrium Constant Dependence on Temperature & Pressure

1. How do temperature and pressure affect the equilibrium constant K?

Temperature and pressure both have a significant impact on the equilibrium constant K. As temperature increases, the value of K also increases for endothermic reactions and decreases for exothermic reactions. This is because an increase in temperature favors the endothermic reaction to absorb more heat and shift the equilibrium towards the products. On the other hand, an increase in pressure will increase the value of K for reactions involving a decrease in the number of moles of gas, and decrease the value of K for reactions involving an increase in the number of moles of gas. This is because an increase in pressure will shift the equilibrium towards the side with fewer moles of gas in order to relieve the pressure.

2. What is the relationship between Kf and Kp?

Kf and Kp are both equilibrium constants, but they are calculated using different variables. Kf is calculated using concentrations of reactants and products, while Kp is calculated using partial pressures of gases involved in the reaction. The relationship between Kf and Kp can be represented by the following equation: Kp = Kf(RT)Δn, where R is the gas constant, T is the temperature in Kelvin, and Δn is the change in the number of moles of gas between reactants and products.

3. How does the equilibrium constant change with temperature?

The equilibrium constant K is directly dependent on temperature. As the temperature increases, the value of K also increases for endothermic reactions and decreases for exothermic reactions. This is because the equilibrium constant takes into account the ratio of products to reactants at a specific temperature. As the temperature changes, the equilibrium shifts to maintain a constant value of K.

4. What is the significance of Kf and Kp in determining the direction of a reaction?

Kf and Kp are both equilibrium constants that indicate the extent to which a reaction has reached equilibrium. A larger value of K indicates that the reaction has shifted towards the products, while a smaller value of K indicates that the reaction has shifted towards the reactants. Therefore, the values of Kf and Kp are crucial in determining the direction of a reaction and whether it is favorable or not.

5. How do changes in pressure affect the equilibrium constant K?

Changes in pressure can have a significant impact on the equilibrium constant K. An increase in pressure will increase the value of K for reactions involving a decrease in the number of moles of gas, and decrease the value of K for reactions involving an increase in the number of moles of gas. This is because an increase in pressure will shift the equilibrium towards the side with fewer moles of gas in order to relieve the pressure. On the other hand, a decrease in pressure will have the opposite effect on the value of K.

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