Out of the two - trans-but-2-ene and cis-but-1-ene, which is more stable and why

Trans-but-2-ene has less heat of hydrogenation than the cis-isomer, therefore it is more stable. 



In the trans isomer, the two methyl groups are present on the opposite side as compared to cis-isomer. As a result, the Vander Waal's forces of attraction in trans isomer are less. This means that the trans isomer has less heat of hydrogenation and is more stable than the cis-isomer.