4.2 g of hydrogen is required to release 1.2 x 10^3 kJ of heat.
Given from the question that 1 mole of hydrogen gas contains 2 g of hydrogen gas.
We also know that heat of combustion per mole of hydrogen gas –285.8 kJ.
From the question, we are told that heat released by the reaction is -1.2 x 10^3 kJ of heat.
Hence;
If 2g of hydrogen releases –285.8 kJ of heat
x g of hydrogen releases -1.2 x 10^3 kJ of heat
x g = 2g x -1.2 x 10^3 kJ / –285.8 kJ
xg = 4.2 g of hydrogen
Learn more: https://brainly.com/question/1527403
