Question

For each of the following reactions, identify another quantity that is equal to DeltH degree rxn.

Answer 1

Answer:

1) $CH_{4}(g) + 2O_{2}(g) --->CO_{2}(g) + 2H_{2}O(l)$

Enthalpy of combustion.

2) $CH_{4}(g)----> C(g) + 4H(g)$

4x bond energy of C - H

3) $C(graphite) + 2H_{2}(g)--->CH_{4}(g)$

enthalpy of formation of CH₄(g)

4) $C(g) + 4H(g) ---> CH_{4}(g)$

- 4x bond energy of C - H

Explanation:

The enthalpy of reaction is the heat change during the reaction.

It can be:

a) Enthalpy of combustion : the heat change during complete burning of one mole of a substance in presence of oxygen.

$CH_{4}(g) + 2O_{2}(g) --->CO_{2}(g) + 2H_{2}O(l)$

b) Enthalpy of formation: the heat change during formation of one mole of a substance from its constituent elements in their native state.

$C(graphite) + 2H_{2}(g)--->CH_{4}(g)$

c) The difference in the bond energies of reactants and products.

$enthalpy= sumofbondenergiesofreactants-sumofbondenegiesofproducts$

For:

$C(graphite) + 2H_{2}(g)--->CH_{4}(g)$

$Enthalpy=[0]-[4XbondenergyofC-H]=-4XbondenergyofC-H$