What effect do concentration changes have on the reaction rate?
Reactions will occur more rapidly when solutions are more concentrated.
This video shows how the speed of a reaction goes up when more concentrated solutions of reactants are used. Note that increasing reaction rate means the time for the reaction to "finish" will be less.
Q: So why does increasing the concentration increase the rate of a reaction?
A: For reactions to occur, particles of reactants must bump into each other (this is called collision theory ). Concentrated solutions contain more particles. More particles means that particles bump into each other more often, which makes the reaction happen faster.
Hope this helps!