Take the test now! Worked Example: Zinc and Hydrochloric Acid Reaction RateĬonsider an experiment in which we add hydrochloric acid, HCl (aq), to a clean piece of metallic zinc, Zn (s), in an open beaker. When we plot the points of amount of product produced vs time, for the same reaction at two different temperatures, we get a graph like the one shown below: Then, imagine we repeat the experiment, keeping all the variables the same, EXCEPT that we heat the whole system. ![]() 2Īt the start of the experiment, only reactants are present, there are no products yet, so the amount of product is zero.īut after that, measurable amounts of product are produced, and we record the amount of product produced every minute (for example). Imagine an experiment in which we can measure the amount of product being formed in a closed vessel. the change in temperature per unit time.the volume of gas evolved per unit time.How a reaction rate is measured depends on the nature of the reactants and products. Play the game now! Measuring Reaction Rates Some reactions occur very slowly in the dark but much more quickly in light.Įg, methane reacts very slowly with chlorine in the dark, but the rate of reaction is much faster in the presence of ultraviolet light. Intensity of Light affects some reactions.Stirring keeps reactant particles in motion increasing the chances of collision and increasing the rate of reaction. Smaller reactant particles provide a greater surface area 1 which increases the chances for particle collisions so the reaction rate increases.Ī catalyst lowers the activation energy for the reaction so more reactant particles will have the minimum amount of energy required to form products so the reaction rate increases. Increasing the temperature will increase the reaction rates of both endothermic and exothermic reactions, it will also, by Le Chetalier's Principle, affect the equilibrium position. Increasing the kinetic energy of reactant particles also means more of the reactant particles will have the minimum amount of energy required to form products (ie, activation energy) which leads to more successful collisions and therefore increases the reaction rate. Increasing the temperature of a reaction increases the kinetic energy of the particles which increases the number of collisions so the reaction rate increases. Temperature (see also Kinetic Energy (Maxwell-Boltzman) Distribution).Increasing the pressure of a gaseous reaction by reducing the volume of the reaction vessel increases the concentration of reactants and products and increases the number of collisions. ![]() Increasing the partial pressure of a gaseous reactant by adding more reactant gas particles increases the concentration of this gaseous reactant and therefore increases the number of collisions so the reaction rate increases. Increasing the concentration of reactants in solution increases the number of reactant particles which increases the number of collisions so the reaction rate increases. Use the PhET Reactions
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