Whats the process of solving this?

Question

A chemist measures the enthalpy change ΔH during the following reaction:

2Na+Cl2→2NaCl ΔH=-822KJ

Use this information to complete the table below. Round each of your answers to the nearest kJ/mol.

NaCl→Na+1/2Cl2

4Na+2Cl2→4NaCl

2NaCl→2Na+Cl2

Answer 1

Multiply the equation by a number in order to reach the new equations. If you multiply an equation by a number, the enthalpy of the reaction changes in proportion. If a reaction is reversed, you need to multiply by a negative.

For example, the first reaction is the given reaction times -1/2 , so the ΔH for the reaction is -(1/2)(822) = 411 kJ