Answer:
There are many types of chemical reactions. In this chapter we will begin with combustion
reactions and end with oxidation/reduction reactions. Along the way we examine various aspects
of reactions.
Homework from the book:
Exercises: 1, 4, 6, 8, 9, 11,12, 14-19, 23, 25, 26, 29
Questions: none
Problems: none
In the study guide: Multiple 4, 5, 6, 12-18.
There are many types of chemical reactions. In this chapter we will begin with combustion
reactions and end with oxidation/reduction reactions. Along the way we examine various aspects
of reactions.
Combustion reactions:
All combustion reactions fall into the pattern:
fuel + O2 → CO2 + H2O
The coefficients of the balanced equation will change depending on the fuel. The fuel can be
almost anything including methane (CH4), propane (C3H8), butane (C4H10), octane (C8H18) or
sugar (C6H12O6).
The balanced equation for methane is CH4 + 2 O2 → CO2 + 2 H2O
The balanced equation for octane is
2 C8H18 + 25 O2 → 16 CO2 + 18 H2O
The combustion of methane or octane is exothermic; it releases energy.
CH4 + 2 O2 → CO2 + 2 H2O + energy
The energies of the products are lower than the energiies of the reactants. The excess energy is
released as heat and light.
Matter tends to move to lower energy states. A good analogy for a reaction is a ball falling down
a hill. Exothermic reactions are more likely to occur. Endothermic reactions absorb energy. In
these reactions the products are higher in energy than the reactants. Endothermic reactions are
less likely to occur. You seldom see a ball spontaneously going uphill. Endothermic reactions
can occur when entropy drives the reaction (pushes the ball up the hill). These reactions are far
less common. An exothermic reaction occurs in a chemical hot pack. (Skiers know about hand
and foot warmers.) An endothermic reaction occurs in a chemical cold pack.
