Rate of Reaction

UNDERSTANDING RATE OF REACTION

Scientific concept

The rate of a reaction is the speed at which a chemical reaction happens. If a reaction has a low rate, that means the molecules combine at a slower speed than a reaction with a high rate. Some reactions take hundreds, maybe even thousands, of years while others can happen in less than one second. Examples of very slow reaction that takes place in plants and ancient fish to become fossils (carbonization). The rate of reaction also depends on the type of molecules that are combining. If there are low concentrations of an essential element or compound, the reaction will be slower. 

Rates of reaction involves collision theory. The collision theory says that as more collisions in a system occur, there will be more combinations of molecules bouncing into each other. If you have more possible combinations there is a higher chance that the molecules will complete the reaction. The reaction will happen faster which means the rate of that reaction will increase.

Reactions take place as a result of particles (atoms or molecules) colliding and then undergoing a reaction. Not all collisions can cause reaction, even in a system where the reaction is spontaneous. When temperature of a system is high, the molecules bounce around a lot more. They have more energy. When they bounce around more, they are more likely to collide. That fact means they are also more likely to combine. When lowering the temperature, the molecules are slower and collide less.  

If there is more of a substance in a system, there is a greater chance that molecules will collide and speed up the rate of the reaction. If there is less of substance, there will be fewer collisions and the reaction will probably happen at a slower speed.

Pressure affects the rate of reaction, especially in the gases. When increasing the pressure, the molecules have less space in which they can move. That greater density of molecules increases the number of collisions. When decreasing the pressure, molecules don't hit each other as often and the rate of reaction decreases.