Factors that Affect Rates of Reactions

There are 5 factors that affect the rates of reactions. They are:

Temperature – as the temperature increases, the rate of the reaction goes up (it gets faster). This is why food stays fresher in the refrigerator. Decreasing the temperature slows down the reactions (biological reactions inside bacteria and molds) involved in rotting. Why?

Concentration – as the concentration of the reactants increases, the rate of the reaction goes up. This is why people blow on campfires. The increase in the amount of oxygen allows the fire to burn faster and hotter. Why?

Surface area – as the surface area of the reactants increases, the rate of the reaction goes up. Why?

Presence of a catalyst – catalysts make the rate of a reaction go up. You may have seen this in a biology class if you put hydrogen peroxide on a piece of liver. Hydrogen peroxide slowly breaks down into water and oxygen gas. However in the presence of certain enzymes, the reaction becomes dramatically faster. Why?

Nature of the reactants – some reactants are less stable than others and will therefore react more readily and more quickly. This is NOT something that you can control (like the others), it is just a way of acknowledging that not all reactions occur at the same rate even if the other conditions are the same. A simple example is that when sodium is placed water it produces hydrogen gas and heat (single displacement reaction). When iron is placed in water it produces hydrogen gas and heat. However, sodium reacts so quickly that enough heat is released to ignite the hydrogen resulting in an explosion. Iron, on the other hand reacts so slowly that no measurable change in the water occurs at all. Why?