Reaction Rates What factors influence the rate of chemical reactions? How do systems in equilibrium respond to change?

Day 1: Reaction Rates Reaction Rate refers to the speed at which reactants in a chemical reaction are changed to products. Reaction rates can be explained by the kinetic theory of matter (matter is made up of atoms or molecules). Reaction rates increase when collisions between molecules or atoms in a substance increase.

Day 1: Reaction Rates The factors that affect reacti0n rate are: Concentration of the reactants. (more particles to collide with) Pressure on the reactants (squeezes particles together allowing more collisions) Temperature of the reactants. (particles move faster and collide more often, just like on the highway.) Surface area – more surfaces mean more collision sites for particles. Solubility – the maximum amount of solute that can dissolve in a solvent.

Day 1: Reaction Rates The factors that affect reacti0n rate are: Ph – acidity of substance can sometimes increase reaction rates. Catalysts – are substances that help speed up a reaction but are not used up in a reaction. Substances that slow reactions are called inhibitors. Enzymes are proteins that serve as biological catalysts.

Day 1: Equilibrium Equilibrium is a state in which the forward and reverse paths of a reaction occur at the same rate. Most chemical reactions are reversible. When a change is introduced to a system in equilibrium, the equilibrium shits in the direction that relieves the change. Example: when the top is removed from a carbonated drink, the system is no longer at equilibrium, and CO2 leaves as bubbles.

Equilibrium

Day 2: Practice Problems 1. Most chemical reactions proceed faster if the reactants are heated. How does the added heat affect reactant atoms or molecules? Answer: Addition of heat causes the particles to move faster and collide more often. The increase in collisions speeds up the reaction. 2. Which of the following changes will not increase the rate of a chemical reaction? A. using an enzyme in a reaction B. adding an inhibitor to the reaction mixture C. increasing the concentration of the reactants D. grinding a solid reactant to make a fine powder Answer: B

Day 2: continued 3. In each of these reactions, the chemical energy increases and then decreases, during the course of the reaction. What does the height of the “hill” on each graph represent? A. energy that must be added to start the reaction B. energy released as reactant molecules approach one another C. the potential energy of the chemical bonds in the molecules of the reactants D. The change in total chemical energy between the reactants and the products Answer: A

Day 3: Understanding Concepts 4. The reaction of glucose and oxygen to form carbon dioxide and water produces the same amount of energy inside living cells as it does by combustion. Analyze how this reaction can occur at body temperature in the cells, but not in the open air. Answer: Inside living cells, enzymes act as catalysts to reduce the amount of energy needed to start the reaction and to allow it to proceed at a lower temperature.

Day 3: Practice Questions Use the kinetic theory of matter to explain how increasing temperature increase the rate of chemical reactions. During a lab, one student adds a chunk of zinc to hydrogen chloride. The other student add the same mass of zinc but in tiny pieces. Which reaction occurs faster and why?

Day 3: Practice Questions In the reaction below, an increase in temperature favors the formation of nitrogen dioxide (NO2). What happens when the chemicals are put in an ice bath. 2NO2 N2O4 + energy

Day 3: Answers Increasing temperature makes the molecules and atoms move faster increasing their chance of collisions. Collisions can lead to reactions between different particles. The crushed up zinc. More surface area for particles to collide. The equilibrium will shift and more N2O4 will form.

Day 4: Quiz (Vamos!!!)