When H2(g) reacts with O2(g) to form H2O(g) , 242 kJ of energy are evolved for each mole of H2(g) that reacts. Write a balanced thermochemical equation for the reaction with an energy term in kJ as part of the equation. Note that the answer box for the energy term is case sensitive. Use the SMALLEST INTEGER coefficients possible and put the energy term (including the units) in the last box on the appropriate side of the equation. If a box is not needed, leave it blank. 2H2 + O2 + 2H2O + An error has been detected in your answer. Check

2H2(g) + O2(g) > 2H2O(g). ∆H= -242KJmol-1

Explanation:

A thermochemical equation is a balanced chemical reaction equation that includes the physical states of all reactants and products and the energy change.

As shown above, hydrogen reacted with oxygen in the gas phase to form water, an energy of 242KJ was evolved and we are required to put this in a thermochemical equation using the least coefficients.

Hydrogen reacts with oxygen to form water in the gas phase in a least ratio of 2:1 as shown in the answer.

The term 'energy evolved' in the question means that the reaction is exothermic and energy is evolved. Hence ∆H is negative as shown.

your answer is a. the enthalpy of formation for a pure element in its standard state is always positive.