Chapter 6, Section 2 Chemical Reactions

“Shame on you, Mrs. Miller, you should be more specific!” Demo: What will happen when lemon juice/salt mixture is applied to various metal objects? Hypothesis: Materials: Procedure: 1. Combine “a few” spoonfuls of lemon juice and salt. 2. Sprinkle over various pieces of metal. 3. Wait (a few days) and observe. “Shame on you, Mrs. Miller, you should be more specific!”

Chemical Reactions A chemical reaction is the process by which atoms or groups of atoms in substances are reorganized into different substances. Clues that a chemical reaction has taken place include the production of heat or light, and formation of a gas, liquid, or solid.

How do you know the difference? Chemical Change Physical Change Alters a substance’s appearance, but not its composition. Same substance before AND after Ex) water boiling/freezing, paper crumbling, chopping wood, crushing a can, mixing sand and water Alters chemical makeup New substance(s) created Ex) rust, burning of wood, metabolizing food, baking a cake, using a battery

Chemical Equations Chemical formulas describe the substances in the reaction and arrows indicate the process of change. Reactants are the starting substances, on the left side of the arrow. Products are the substances formed during the reaction, on the right side of the arrow.

For Example: Glucose and oxygen react to form carbon dioxide and water. Label the reactants and products

Balanced Equations The law of conservation of mass states matter cannot be created or destroyed. The number of atoms of each element on the reactant side must equal the number of atoms of the same element on the product side.

Practice: Balance the following chemical equations: K + B203  K2O + B HCl + NaOH  NaCl + H2O CH4 + O2  CO2 + H2O N2 + H2  NH2 Al + S8  Al2S3 RUST DEMO: ___ O2 + ___ Fe  ___ Fe2O3

Energy of Reactions

Energy of Reactions The activation energy is the minimum amount of energy needed for reactants to form products in a chemical reaction.

This reaction is exothermic and released heat energy. The energy of the product is lower than the energy of the reactants.

This reaction is endothermic and absorbed heat energy. The energy of the products is higher than the energy of the reactants.

Endothermicvs. Exothermic Demo

Enzymes Catalyst - a substance that lowers the activation energy needed to start a chemical reaction. It does not increase how much product is made and it does not get used up in the reaction. Enzymes – proteins that serve as biological catalysts.

Enzymes

Enzyme-Substrate Complex The reactants that bind to the enzyme are called substrates. The specific location where a substrate binds on an enzyme is called the active site.

Lock and Key Model

Enzyme-Substrate Complex The active site changes shape and forms the enzyme-substrate complex, which helps chemical bonds in the reactants to be broken and new bonds to form. Factors such as pH, temperature, and other substances affect enzyme activity.

Journal What role do enzymes play in living things? How do they help maintain homeostasis? Enzymes lower the activation energy, which speeds up chemical reactions and cellular processes. They help in maintaining homeostasis by making sure the body’s needs are met.

Thought Question Which of the following best explains why enzymes are necessary for many cellular reactions? Enzymes supply the oxygen necessary for the reactions. Enzymes change reactants from solid to liquid during the reactions. The reactions take up too much space in the cell if enzymes are missing. The reactions are too slow to meet the needs of the cell if enzymes are missing.

Journal Draw a diagram of a roller coaster and write a paragraph relating the ride to activation energy and a chemical reaction.