Chemical Reactions, cont’d

Absorbs energyReleases energy

Endothermic Reaction

Exothermic Reaction

What happens to energy in a reaction?

Reactants Products

Reaction energy (Q) = energy absorbed – energy released

Single bonds energies (kJ/mol)

CH4 H2ONH3

How much energy is contained in the bonds of the following molecules?

Double and triple bonds energies (kJ/mol)

What are some examples of endothermic and exothermic reactions?

CH4 + 2 O2 CO2 + 2 H2O

• How much energy is absorbed to break the bonds of the reactants during the chemical reaction?

• How much energy is released in the formation of the products?

• What is the reaction energy (Q)?• Is this reaction endothermic or exothermic?

+ 686 kJ

Ener

gy (k

J)

2 H2O 2 H2 + O2

• How much energy is absorbed to break the bonds of the reactants during the chemical reaction?

• How much energy is released in the formation of the products?

• What is the reaction energy (Q)?• Is this reaction endothermic or exothermic?

N2 + 3 H2 2 NH3

HCCH + 2 HF CH3CHF2

2 H2O + O2 2 H2O2

N2 + 3 H2 2 NH3

HCCH + 2 HF CH3CHF2

2 H2O + O2 2 H2O2

Combining reaction energy & stoichiometry

N2 + 2 O2 + 67.7 kJ 2 NO2

What amount of energy is required to produce 8 moles of NO2?

Combining reaction energy & stoichiometry

CH4 + 2 O2 CO2 + 2 H2O + 686 kJ

How much energy will be produced by the above reaction if 32 g of methane (CH4) react?

Combining reaction energy & stoichiometry

C + O2 CO2 + 393.5 kJ

The complete combustion of 1 mole of carbon releases 393.5 kJ of energy. To obtain 1000 kJ of energy, what mass of carbon will need to be burned?