Energy can neither be created nor destroyed.
Energy is conserved in the universe
Energy change in a cyclic process is 0.
Take the problem:$^1$
A beaker with 100 ml of water is heated due to the combustion of 29 grams of butane with oxygen. The initial temperature is 25 and the final temperature is 40. What is the molar combustion enthalpy change($\Delta H^{\minuso}_c$)? Assume that the beaker does not absorb any energy.