I have to write the rate law for two elementary reaction equations

A ) 2a+b>c+d

B ) X+Y>Z

I'm pretty sure it's just k[ A ][ B ] and k[ X ][ Y ] but does the coefficient affect it in this case? is it [ A ]^2 ?

To write the rate law for the given elementary reaction equations, you need to consider the stoichiometry of the reaction and determine the order of each reactant involved. The rate law expresses the relationship between the rate of a reaction and the concentrations of the reactants.

Let's analyze each reaction individually:

A) 2a + b -> c + d

To write the rate law for this reaction, you need to determine the rate-determining step or the slowest step of the reaction. Assuming this is an elementary reaction and the formation of the products is dependent on the reactants, the rate-determining step corresponds to the formation of product c and d.

The rate of this reaction can be written as follows:
rate = k[A]^m[B]^n

Since the coefficients represent the stoichiometry of the reaction, they also indicate the order of the reactants in the rate law. In this case, the coefficient of 'a' is 2, suggesting that the order with respect to 'A' is 2. The coefficient of 'b' is 1, indicating an order of 1 with respect to 'B'.

Hence, the rate law for this reaction is given by:
rate = k[A]^2[B]^1 or simply rate = k[A]^2[B]

B) X + Y -> Z

Similarly, for this reaction, the rate law can be written as:
rate = k[X]^m[Y]^n

If the coefficients of X and Y are both 1, it implies that the order of both X and Y is 1.

Therefore, the rate law for this reaction is:
rate = k[X]^1[Y]^1 or simply rate = k[X][Y]

In summary, for the given elementary reactions:
A) Rate law: rate = k[A]^2[B]
B) Rate law: rate = k[X][Y]

It's important to note that the coefficients in the balanced chemical equation do affect the rate law and indicate the order of the reactants in the rate equation. The exponents in the rate law equation reflect the order of each reactant, which is often different from the stoichiometric coefficients.