# A2 Rate equation Chemistry Question

Can anyone help me with this question? The answer is C

Solutions of two compounds, W and X, react together in the presence of a soluble catalyst, Y, as shown in the equation
2W + X Z
When the concentrations of W, X and Y are all doubled, the rate of reaction increases by a
factor of four.
Which is a possible rate equation for this reaction?
A rate = k [W]^2[X]
B rate = k [W]^2[Y]
C rate = k [X] [Y]
D rate = k [X] [Z]
Can't be A because since W is order 2 and X is order 1 there, and [X] and [W] double, the rate of reaction would multiply by 2^2 * 2 = 8, rather than 4.
Same goes for B, just think about it with Y instead of X.
C is correct, because doubling 2 order 1 reactants will each have the effect of doubling the rate - so since 2 things double the rate, the rate multiplies by 2*2 = 4.
D is wrong because Z isn't a reactant so can't be in the rate equation.
Original post by MedicPls
Can't be A because since W is order 2 and X is order 1 there, and [X] and [W] double, the rate of reaction would multiply by 2^2 * 2 = 8, rather than 4.
Same goes for B, just think about it with Y instead of X.
C is correct, because doubling 2 order 1 reactants will each have the effect of doubling the rate - so since 2 things double the rate, the rate multiplies by 2*2 = 4.
D is wrong because Z isn't a reactant so can't be in the rate equation.

thank so much , extremely useful even 3 years later
Original post by MedicPls
Can't be A because since W is order 2 and X is order 1 there, and [X] and [W] double, the rate of reaction would multiply by 2^2 * 2 = 8, rather than 4.
Same goes for B, just think about it with Y instead of X.
C is correct, because doubling 2 order 1 reactants will each have the effect of doubling the rate - so since 2 things double the rate, the rate multiplies by 2*2 = 4.
D is wrong because Z isn't a reactant so can't be in the rate equation.

as the person above me said, thanks so much!