Given that H2 (g) + F2 (g) ⟶ 2HF (g) ΔH ∘ rxn = − 546.6 kJ 2H2 (g) + O2 (g) ⟶ 2H2O (l) ΔH∘rxn = − 571.6 kJ calculate the value of ΔH∘rxn for 2F2 (g) + 2H2O (l) ⟶ 4HF (g) + O2 (g)

Answer : The value of for the reaction is, -521.6 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 given main reaction is,

The intermediate balanced chemical reaction will be,

(1)    

(2)    

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

(1)    

(2)    

The expression for enthalpy of change will be,

Thus, the value of for the reaction is, -521.6 kJ

it can be observed without changing the identity of the object.

it depends on what substance you're talking about as well as many other factors. in quantum mechanics, the observation of particles affects the observers ability to measure certain properties. for example: you can know the velocity of a particle, but you can't know it's position; or you can know it's position, but not it's velocity. it's like trying to find out where a grain of sand is by throwing other grains of sand at it. once you find out where it is, it's been moved. it's also like trying to find an answer to the question of whether or not a tree falling in a forest makes a sound if nobody is there to hear it. paradoxically, the only way to find out is to be there and hear it.