The student concludes that the rate of reaction is greater when the concentration of hydrochloric acid is higher. Why is the rate of reaction greater when the concentration of hydrochloric acid is higher? Select two options.

According to collision theory, for a reaction to occur, reactant particles must collide with sufficient energy. The rate of reaction depends on the frequency of these successful collisions. - **Higher concentration** means that there are **more reactant particles in the same volume**. (This is the definition of concentration). - Because the particles are more crowded, they will collide with each other and with the magnesium more often. This means **there are more particle collisions each second** (an increased frequency of collisions). - An increased frequency of collisions leads to an increased frequency of successful collisions, and therefore a faster rate of reaction. - The speed and energy of the particles are determined by the temperature, which is a control variable in this experiment.