Question

could you please check my work? thanks.

<b>For the reaction between reactants A and B below, if 4.925 moles of A is placed into a flask with excess B it is found that the amount of A remaining after 6.85 seconds is 2.737 moles.

2A (g) + B (g)-----> 3 C (g)

a. find the rate of reaction with respect to A (in Ms^-1)
b. find the rate of the reaction with respect to B
c. find the reate of the reaction with respect to C </b>

so far i have for part a:
rate = delta [A]/delta t
i calculated the molarities of before and after:
4.925mols/3.00L = 1.64 M
2.727mols/3.00L = .912 M

delta M = .728
but that's supposed to be negative because the number of mols decreases correct?
so i got -.728 M

delta t = 6.85 (0 to 6.85 seconds)

so rate a = -(.728M/6.85 seconds)
but since reactants are involved it should be negative on the outside too, so it's
=-(-.728M/6.85 s)
=.106 Ms^-1

is that correct????
to find b woul i just divide the mols of A by two????