Given that H2(g) + F2(g) - > 2HF(g) delta H rxn = -546.6 kJ 2H2(g)+ O2(g) - > 2H2O(l) delta H rxn = 571.6 kJ calculate the value of delta H rxn for 2F2(g)+2HO(l) - > 4Hf(g)+O2(g)

Answer : The value of for the reaction is, -1664.8 kJ

Explanation :

According to Hess’s law of constant heat summation, the heat absorbed or evolved in a given chemical equation is the same whether the process occurs in one step or several steps.

According to this law, the chemical equation can be treated as ordinary algebraic expression and can be added or subtracted to yield the required equation. That means the enthalpy change of the overall reaction is the sum of the enthalpy changes of the intermediate reactions.

The main reaction is,

The intermediate balanced chemical reaction will be,

(1)    

(2)    

Now we are reversing reaction 2 and multiplying reaction 1 by 2 then adding both the equations, we get :

(1)    

(2)    

The expression for enthalpy of the given reaction will be:

Therefore, the value of for the reaction is, -1664.8 kJ

- aluminum and copper chloride.

- the chloride ion to separate the aluminum from the oxygen so that the aluminum can react with the copper ions (and the water molecules).

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