When the equation, H2S + O2 ---> H2O + SO2, is completely balanced
using the smallest whole-number coefficients, what is the sum of all
the coefficients?
a. 5
b. 7
c. 9
d. 11

Hi teatea!!

You can balance this equation by sucesive inspections:

nH2S + mO2 ---> qH2O + pSO2

In the left side you have an even number of atoms of O. So the H2O
molecule must have an even number as coefficient, we are looking for
the smallest so we will try with the smallest one: 2.

nH2S + mO2 ---> 2H2O + pSO2

Now we have at least 4 atoms of H in the right side, so n can be 2:

2H2S + mO2 ---> 2H2O + pSO2

Now there are 2 atoms of S in the left side, so try with p = 2 :

2H2S + mO2 ---> 2H2O + 2SO2

Now we find a total of 6 atoms of O in the right side, so m must be 3:

2H2S + 3O2 ---> 2H2O + 2SO2

This equation cannot be reduced, so it is the balanced equation, and
the sum of all the coefficients is 2+3+2+2 = 9.

The correct answer is c.

For more info see "Balancing Chemical Reaction Equations" from the
Department of Chemistry, California State University, Sacramento
website:
http://www.chem.csus.edu/poster/bal/bal.htm

Hope this helps.

regards.
livioflores-ga