Given the reaction, h2 + cl2 → 2hcl, if 12.0 moles of hcl were made, then how many moles of h2 were used?
24.0 moles
12.0 moles
6.00 moles
3.00 moles

C

Explanation:

Balance the equation

It is balanced.

Put the known number of moles under the HCl

H2 + Cl2 → 2HCl

                     12

Put an x under the desired unknown.

H2 + Cl2 → 2HCl

  x                  12

Set up a proportion

1/x = 2/12

Solve

Cross multiply

2x = 1 * 12

2x = 12                   Divide by 2

2x/2 = 12/2

x = 6

The answer is C  

your answer is a. the enthalpy of formation for a pure element in its standard state is always positive.