Calculate the amount of energy released when 500 cm³ of methane gas at STP reacts with excess air according to the equation:
How you find the moles from volume? Did you assume $500\ \mathrm{cm^{3}}$ is $500\ \mathrm g$? This is wrong, because the density of $\ce{CH4}$ is not $1\ \mathrm{g/cm^{3}}$. You have to use another way to calculate moles of the gas. Think about ideal gas law or how much volume for STP gas.