Question

For the combustion of 1 mole of methane, -213 calories. How many calories are given off when 27 grams of oxygen is burned with excess methane?

Answer 1

first write down balanced chemical equation of combustion of methane, then from reaction ratio calculate how much methane can react with 27 g of oxygen, and then just multiply moles of methane with -213 cal/mol, that's all folks ;)