Question

Consider the reaction:
8H2S(g)+4O2(g)?8H2O(g)+S8(g)
?[H2S]/?t = -0.047M/s .

Find ?[O2]/?t

Express your answer to two significant figures and include the appropriate units

Find ?[H2O]/?t

Express your answer to two significant figures and include the appropriate units.

Find ?[S8]/?t

Express your answer to two significant figures and include the appropriate units.

Find the rate of the reaction.

Express your answer to two significant figures and include the appropriate units.

Answer 1

Consider a reaction 2A + B -> C, in which one mole of C is produced from every 2 moles of A and one mole of B. The rate of this reaction may be described in terms of either the disappearance of reactants over time, or the appearance of products over time:

rate = (decrease in concentration of reactions)/(time) = (increase in concentration of products)/time

Because the concentration of a reactant decreases during the reaction, a minus sign is placed before a rate that is expressed in terms of reactants. For the reaction above, the rate of reaction with respect to A is -?[A]/?t, with respect to B is -?[B]/?t, and with respect to C is ?[C]/?t. In this particular reaction, the three rates are not equal. According to the stoichiometry of the reaction, A is used up twice as fast as B, and A is consumed twice as fast as C is produced. To show a standard rate of reaction in which the rates with respect to all substances are equal, the rate for each substance should be divided by its stoichiometric coefficient.

Rate = -(1/2)(?[A]/?t) = -?[B]/?t = ?[C]/?t ..."



So for your reaction, we have the following relationships:

8H2S(g)+4O2(g)?8H2O(g)+S8(g)

rate = -(1/8)?[H2S]/?t = -(1/4)?[O2]/?t = +(1/8)[H2O]/?t = +(1)?[S8]/?t

Just pick out the appropriate relationship, solve for the desired rate, and substitute the given value (?[H2S]/?t = -0.057 M/s).

For example, for (A):

A) Find ?[O2]/?t )

We have from the relationships

-(1/8)?[H2S]/?t = -(1/4)?[O2]/?t

Solve for ?[O2]/?t:

-(1/8)?[H2S]/?t = -(1/4)?[O2]/?t
(1/8)?[H2S]/?t = (1/4)?[O2]/?t
(4)*((1/8)?[H2S]/?t) = (4*)((1/4)?[O2]/?t)
(1/2)?[H2S]/?t = ?[O2]/?t
(1/2))*( -0.057 M/s) = ?[O2]/?t
?[O2]/?t = -0.0285 M/s