Question

Part A
For which of the following reactions is ΔH∘rxn equal to ΔH∘f of the product(s)?

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Check all that apply.
Li(s)+12Cl2(g)→LiCl(s)

2Li(s)+Cl2(g)→2LiCl(s)

2H2(g)+O2(g)→2H2O(g)

H2(g)+12O2(g)→H2O(g)

H2O2(g)→12O2(g)+H2O(g)

Li(s)+12Cl2(l)→LiCl(s)

Answer 1

The standard enthalpy of formation is defined as the change in enthalpy when one mole of a substance in the standard state (1 atm of pressure and 298.15 K) is formed from its pure elements under the same conditions. Standard state elements or molecules will always have zero enthalpy change.
2Li(s)+Cl2(g) -->2LiCl(s) ---- 2 mol product

2H2(g)+O2(g) --> 2H2O(g) -----2 mol product

Li(s)+12Cl2(l) --> LiCl(s) ------ chlorine is in liquid state

H2O2(g) --> 12O2(g) + H2O(g)

Correct answers:

Li(s) + 1/2Cl2(g) --> LiCl(s)

H2(g) + 1/2O2(g) --> H2O(g)