Question

2(H2O2)->2(H2O)+O2 H=-196kj
calculate the value of q when 5g of H2O2 decompose at constant pressure, why the answer is -14.4kj?

Answer 1

it's proportional. The equation says that 2 moles of H2O2 generates 196 kJ,
2 moles of H2O2 would weigh 68g (add up atomic masses)

So if 68g releases 196 kJ, then less than 1/10 of that mass (5g) would produce less than 1/10 of the energy (14kJ)