1. A(aq) + B(aq) ¡ê C(aq) + D(aq)
Initially, 1 mol of A and 1 mol of B are allowed to react and come to equilibrium. It is found hat there is 0.5 mol of A left at equilibrium. Calculate Kc for the reaction.
how do i work out Kc? when ive done questions b4 ive had volume/conc and the amount of products there are
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Starting mols:
A = 1
B = 1
C = 0
D = 0
equilibrium mols:
A = 0.5
B =
C =
D =
change in mols:
A = -x
B = -x
C = +x
D = +x
Obviously, if we started with 1 mol A and ended up with 0.5 mols A, then the change (what we have labeled x) is 0.5.
Thus change in B is -0.5, change in C is +0.5 and change in D is +0.5
These are mols and not concns and there is no volume listed. Since the mols ratios of the reaction are 1:1:1:1, then we can assume a volume of 1 L which makes the concns and mols the same. Plug into Kc expression and solve for Kc. Check my thinking. I think you can assume ANY value for volume and obtain the same answer for Kc.
To calculate the equilibrium constant, Kc, for a chemical reaction, you need to know the concentrations of the reactants and products at equilibrium. Typically, the equilibrium concentrations are given, but in this case, you are only provided with the amount (in moles) of A remaining at equilibrium.
To calculate Kc, you'll need to determine the concentrations of A, B, C, and D at equilibrium. Since the volume or concentrations are not given, let's assume that the volume is V liters.
Given:
Initial moles of A = 1 mol
Initial moles of B = 1 mol
Moles of A at equilibrium = 0.5 mol
The reaction stoichiometry indicates that one mole of A reacts with one mole of B to form one mole each of C and D. Therefore, at equilibrium:
[A] = (total moles of A - moles of A at equilibrium) / V = (1 - 0.5) / V = 0.5 / V M
[B] = (total moles of B - moles of B at equilibrium) / V = (1 - 0) / V = 1 / V M
[C] = (moles of C at equilibrium) / V = 0 / V = 0 M
[D] = (moles of D at equilibrium) / V = 0 / V = 0 M
Now we can substitute these concentrations into the equilibrium expression for Kc:
Kc = ([C] x [D]) / ([A] x [B])
Since [C] and [D] are both zero, the product of their concentrations is zero. The equation simplifies to:
Kc = 0 / ([A] x [B]) = 0
Therefore, the equilibrium constant for this reaction, Kc, is equal to zero.