How does the rate of change of the product compare to the rate of change of the reactant?

Answer 1

It depends on what the equation of the reaction is, which will determine the order of the reaction

Answer 2

other than that reactants disappear (negative rate of change in concentration) and products appear (positive rate of change in concentration), nothing can be said unless you know the reaction stoichiometry, that is, for a general reaction with reactants A and B, products C and D:

aA + bB -> cC + dD

you need to know the stoichiometric coefficients, a b c and d.

rate can be defined in terms of disappearance of reactants or appearance of products:

rate = -1/a*d[A]/dt = -1/b*d[B]/dt = 1/c*d[C]/dt = 1/d*d[D]/dt

the rate is not constant, contrary to the answer above. one can define a rate coefficient k for the same general reaction:

rate = k*[A]^x*[B]^y

the rate coefficient is independent of concentration but depends on temperature, pressure, and potentially many other things. x and y are the orders of the reaction with respect to A and B, and are not the same in general as the stoichiometric coefficients a and b. they will only be the same if the reaction is elementary, that is the reaction mechanism consists of just the one chemical reaction.

Answer 3

For a given reaction:

aA+bB -> cC + dD

if rA is the reaction rate for reactant A, then the rates for the other reactant and products are:

rB=(b/a) rA
rC=-(c/a) rA
rD=-(d/a) rA

Generalizing, for any given reaction

ri/v = k

where
ri is the reaction rate for a reactant or product
v is the stoichiometric coefficient for that reactant or product (positive for products, negative for reactants)
k is a constant