How many grams of hydrogen gas are produced?

Question

CH3OH --> CO + 2H2.

For a given sample of CH3OH, the enthalpy change on reaction is 17.5kJ.

Answer 1

impossible to tell, unless you tell us how much starting material you had.

If you know g CH3OH, it's just the usual unit conversion:

g CH3OH

x 1 mol CH3OH /(formula mass CH3 OH)

x 2 mol H2/1 mol CH3OH (from reaction equation)

x formula mass (g) H2/mol H2

If you have been told, or have been given enough information to work out, the enthalpy change of the reaction, you can use

17.5 kJ = enthalpy change per mole x number of moles