Consider the following reaction.
CaC2(s) + 2 H2O(l) ⇌ Ca(OH)2(aq) + C2H2(g)
Which of the following represents the thermodynamic equilibrium constant, K ?
K=[H2O]2[CaC2]PC2H2[Ca(OH)2]
K=PC2H2[Ca(OH)2][CaC2]
K=[C2H2][Ca(OH)2][H2O]2[CaC2]
K=PC2H2[Ca(OH)2]
K=[C2H2][Ca(OH)2]
K=[H2O]2[CaC2][C2H2][Ca(OH)2]
i just dont understand how to solve it. will it be K=[C2H2][Ca(OH)2][H2O]2[CaC2]?
No. "pure" solids and "pure" liquids are not part of a K value.
BTW, please don't switch screen names. One name is all you need.
Another BTW, I think there are two answers that are correct.
oh i see, is it K=PC2H2[Ca(OH)2]
i mean K=[C2H2][Ca(OH)2]
I think both of those are correct. Use pC2H2 if partial pressures are given and use M if mols/L are given
To determine the correct expression for the thermodynamic equilibrium constant, K, we need to write the reaction equation and then use the stoichiometry of the reaction to find the correct concentrations of the reactants and products.
The balanced chemical equation for the reaction is:
CaC2(s) + 2 H2O(l) ⇌ Ca(OH)2(aq) + C2H2(g)
Now, let's determine the concentrations of the reactants and products:
- [CaC2] represents the concentration of CaC2(s), which is a solid. However, solids do not appear in the equilibrium constant expression because their concentration remains constant. Therefore, we do not include [CaC2] in the equilibrium constant expression.
- [H2O] represents the concentration of H2O(l), which is a liquid. Similarly, liquids also do not appear in the equilibrium constant expression because their concentration remains constant. Therefore, we do not include [H2O] in the equilibrium constant expression.
- [Ca(OH)2] represents the concentration of Ca(OH)2(aq), which is an aqueous solution. The concentration of Ca(OH)2(aq) does change during the reaction, so we include [Ca(OH)2] in the equilibrium constant expression.
- [C2H2] represents the concentration of C2H2(g), which is a gas. Since gases do appear in the equilibrium constant expression, we include [C2H2] in the equilibrium constant expression.
Now, let's analyze the given answer choices:
K=[H2O]2[CaC2]PC2H2[Ca(OH)2] - Incorrect
This answer choice includes both [H2O] and [CaC2], which we determined should not be included in the equilibrium constant expression.
K=PC2H2[Ca(OH)2][CaC2] - Incorrect
This answer choice includes [CaC2], which we determined should not be included in the equilibrium constant expression.
K=[C2H2][Ca(OH)2][H2O]2[CaC2] - Incorrect
This answer choice includes both [H2O] and [CaC2], which we determined should not be included in the equilibrium constant expression.
K=PC2H2[Ca(OH)2] - Incorrect
This answer choice is missing the reactant concentration [H2O] in the equilibrium constant expression.
K=[C2H2][Ca(OH)2] - Correct
This answer choice includes both [C2H2] and [Ca(OH)2], which we determined should be included in the equilibrium constant expression. It does not include [H2O], which is consistent with our earlier analysis.
K=[H2O]2[CaC2][C2H2][Ca(OH)2] - Incorrect
This answer choice includes [CaC2], which we determined should not be included in the equilibrium constant expression.
Therefore, the correct expression for the thermodynamic equilibrium constant, K, is K = [C2H2][Ca(OH)2].