For the following reaction at equilibrium in a closed vessel, ΔrH = −153 kJ per mol of CH3CHO.
CH3CHO(g) ⇌ CH4(g) + CO(g)
Which of the following statements are correct?
a. For the thermodynamic equilibrium constant, K at 298 K is greater than K at 500 K.
b. At 25 oC, K = Kp
c. Adding a catalyst will not affect the equilibrium partial pressure of CO(g).
d. Adding some CH4(g) will decrease the equilibrium partial pressure of CH3CHO(g).
e. Decreasing the volume of the system will decrease the moles of CO(g) at equilibrium.
f. At 25 oC, Kp < Kc
no idea how to do this
is it b and d?
Why do you believe b and d are correct?
All of these are Le Chatelier's Principle. You should know that b can't be right.. You know that Kp = Kc*RT)^delta n so the only time Kp can equal Kc is when delta n is zero. In this reaction you have 2 mols products and 1 mol reactant so delta n isn't zero. It's 1.
To determine which statements are correct, let's analyze each statement one by one:
a. For the thermodynamic equilibrium constant, K at 298 K is greater than K at 500 K.
To determine the effect of temperature on the equilibrium constant (K), we need to consider the sign of ΔrH. In this case, ΔrH is negative (-153 kJ). According to Le Chatelier's principle, if a reaction is exothermic (negative ΔH), an increase in temperature will shift the equilibrium towards the reactants. Therefore, the equilibrium constant (K) at a lower temperature (298 K) will be greater than at a higher temperature (500 K). So, statement a is correct.
b. At 25 oC, K = Kp.
The equilibrium constant expressed in terms of partial pressure (Kp) can be equal to the equilibrium constant expressed in terms of concentration (Kc) only if the stoichiometry of the balanced chemical equation is such that the number of gas moles remains the same. In this case, since the reaction involves the formation of gases (CH₄ and CO), the number of gas moles changes, and Kp is not equal to Kc. Therefore, statement b is incorrect.
c. Adding a catalyst will not affect the equilibrium partial pressure of CO(g).
A catalyst increases the rate of a reaction but does not affect the position of equilibrium or the equilibrium composition. Therefore, adding a catalyst will not affect the equilibrium partial pressure of CO(g). So, statement c is correct.
d. Adding some CH₄(g) will decrease the equilibrium partial pressure of CH₃CHO(g).
According to Le Chatelier's principle, adding a reactant to a reaction at equilibrium will shift the equilibrium position in the direction that consumes the added reactant. In this case, if we add CH₄(g), which is a product, the equilibrium will shift towards the reactants CH₃CHO(g). As a result, the equilibrium partial pressure of CH₃CHO(g) will increase, not decrease. Therefore, statement d is incorrect.
e. Decreasing the volume of the system will decrease the moles of CO(g) at equilibrium.
Decreasing the volume of a gas system will increase the partial pressure of the gases present, according to Boyle's law. In this case, decreasing the volume will increase the partial pressure of CO(g) at equilibrium as it is a product of the reaction. Therefore, statement e is incorrect.
f. At 25 oC, Kp < Kc.
This statement is not directly related to the given reaction and its thermodynamic data. Without specific information about the balanced equation, it is not possible to determine whether Kp is greater or smaller than Kc at 25 oC. Therefore, statement f is inconclusive.
Based on the analysis, the correct statements are:
a. For the thermodynamic equilibrium constant, K at 298 K is greater than K at 500 K.
c. Adding a catalyst will not affect the equilibrium partial pressure of CO(g).