Question

Part A:

The decomposition of NI3 to form N2 and I2 releases −290.0 kJ of energy. The reaction can be represented as

2NI3(s)→N2(g)+3I2(g), ΔHrxn=−290.0 kJ

Find the change in enthaply when 15.0 g of NI3 decomposes.

Express your answer to three significant figures and include the appropriate units.

Part B:

4NH3(g)+5O2(g)→4NO(g)+6H2O(g)

Calculate the standard heat of reaction, or ΔH∘rxn, for this reaction using the given data. Also consider that the standard enthalpy of the formation of elements in their pure form is considered to be zero.

Reactant or product	ΔH∘f (kJ/mol)
NH3(g)	-45.9
NO(g)	91.3
H2O(g)	-241.8

Express your answer to four significant figures and include the appropriate units.

Answer 1

2NI3(s)→N2(g)+3I2(g), ΔHrxn=−290.0 kJ

2 moles of NI3 to gives -290Kj

2*394.72g of NI3 to gives -290KJ

15g of NI3 to gives        = -290*15/2*394.72   =-5.51KJ

part-B

4NH3(g)+5O2(g)→4NO(g)+6H2O(g)

ΔH∘rex    = ΔH∘f products - ΔH∘f reactant

                = 6*-241.8+4*91.3-(4*-45.9+5*0)

                = -902.0KJ