Chapter 7.4 – Reaction Rates chemical reactions can happen at different rates anything that increases contact between particles increases the rate of reaction at higher temperatures particles move faster because faster particles move more, they have a higher chance to collide and react therefore reactions are faster at higher temperatures

Chapter 7.4 – Reaction Rates increasing the surface area of a reactant increases the rate of a reaction there are more particles exposed to collide with if we add more particles to the same volume, the particles will collide more often increasing concentration of reactants speeds up reactions at high pressure gases are closer together so they collide more high pressure increases reaction rates

Chapter 7.4 – Reaction Rates more massive particles move slower than smaller ones at the same temperature smaller particles react faster than larger particles catalyst – a substance that changes the rate of a chemical reaction without being consumed or changed significantly most solid catalysts speed up reactions by providing a place for reactants to gather and react catalysts that slow reactions are called inhibitors

Chapter 7.4 – Reaction Rates enzyme – catalyst for chemical reactions in living things is a molecule such as a protein or RNA each different enzyme controls one reaction they are very fragile substrate – reactant in reactions catalyzed by enzymes - a substrate fits into the active site on an enzyme and undergoes a reaction

Chapter 7.4 – Reaction Rates some reactions can go in both directions they are called reversible reactions chemical equilibrium – a state of balance in which the rate of the forward reaction equals the rate of the reverse reaction and the concentrations of products and reactants remain unchanged - a system in equilibrium responds to change by doing whatever is required to get back to equilibrium

Chapter 7.4 – Reaction Rates this means the reaction starts going more in one direction than the other Le Chatelier’s principle – if a change is made to a system in chemical equilibrium, the equilibrium shifts to oppose the change until a new equilibrium is reached - when we say favors the reaction that means we make more of that side

Chapter 7.4 – Reaction Rates things that change effect on equilibrium temperature increasing temperature favors the reaction that absorbs energy pressure increasing pressure favors the reaction that produces fewer molecules of gas concentration increasing the concentration of one substance favors the reaction that produces less of that substance

Chapter 7.4 – Reaction Rates the Haber process converts nitrogen from the air to ammonia used in fertilizer and plastics N2(g) + 3H2(g) ↔ 2NH3(g) + heat if we increase temperature, energy is absorbed on the left, so the reaction moves left, and we make more reactants if we increase pressure, there is fewer moles of gas on the right, so the reaction moves right, and we make more product if we increase the amount of NH3, the reaction moves left, and we make more reactants