In a phase change of water between the liquid and the gas phases, 770.1 kJ of energy was released by the system. What was the product, and how much of it was formed in the phase change? (Data: H2O(l) → H2O(g) ΔH = 44.01 kJ/mol.)

In this question, we are asked to name the product formed during a phase change and also state the amount of this product formed during the phase change.

Firstly, we write the reaction equation;

H20(l) ——-> H20(g) ΔH= 44.01 kJ/mol

Since heat change is given as positive, this means the reaction is endothermic i.e heat is absorbed by the syatem to change state from liquid to gas.

Thus, when 770 KJ of heat is released by the system then state changes from gas to liquid.

This means that the product required is water.

Now as 44 KJ is required to have conversion of 1 mole

then for 770 KJ we need = (1/44)* 770

= 17.5 moles of liquid water where the number 44 is the molar mass of water

This means that 17.5 moles of liquid water are formed.