Calculate the enthalpy of formation of water.Is the reaction an exothermic or endothermic reaction?
The reaction is as follows:
2H2 + O2 -> 2H2O
This means that for every 2 molecules of Hydrogen gas, one molecule of Oxygen is needed to make 2 molecules of water
To calculate the enthalpy of this reaction, we use the equation:
Enthalpy of reaction = (Enthalpy of products) - (Enthalpy of reactants)
The Enthalpy of Formations for each molecules are:
H2 =0kJ/mol
O2 =0kJ/mol
H2O=-285.83kJ/mol
From the equation given earlier, we can put the numbers in and get
Enthalpy= -285.83-(0+0)
This means Enthalpy of formation of water=-285.83kJ/mol
So how can we tell if its endothermic or exothermic?
It's really quite simple. If there is a negative (minus) sign, the reaction is exothermic, and if there is a positive (plus) sign, the reaction is endothermic!
Therefore we can see, our answer has a negative sign so is exothermic!
