Chemical Reactions

Remember the Krebs Cycle? The Citric Acid Cycle is also known as the Krebs Cycle or Tricarboxylic Acid (TCA) Cycle. It is a series of chemical reactions that takes place in the cell that breaks down food molecules into carbon dioxide, water, and energy.

Chemical Reactions We know that electrons make bonds. We know that bonds make chemicals. What do chemicals do?

What do you already know about chemical reactions? With your neighbors list at least 3 things you already know about chemical reactions. They create chemical changes. New, different chemicals are formed. They break/form chemical bonds. Atoms can’t be created or destroyed.

Chemical Reaction: the process by which one or more substances are changed into one or more different substances. Chemical reactions create new chemicals. They do this by breaking/re-forming chemical bonds.

What happens when Hydrogen (H 2 ) and oxygen (O 2 ) come together to create water (H 2 O)? I have the same number of each atoms on each side. Green bonds are bonds that get broken. Red bonds are bonds that are re-formed. I have different chemicals on both sides of the reaction.

Signs of a Chemical Reaction

1.Color changes - Different combinations of molecules reflect light differently. A color change indicates a change in molecules. 2.Heat content changes - In all chemical reactions, the heat content of the reactants and the content of the products is never the same. Sometimes the difference is great and can be easily detected; at other times the difference is slight and is more difficult to detect.

Signs of a Chemical Reaction 3.A gas is produced - Whenever a gaseous product forms in a liquid solution, bubbles can be seen. A colorless gas produced in a reaction of solids is much harder to detect. 4.A precipitate forms - Precipitates are insoluble products formed by a reaction taking place in a liquid solution. This insoluble product will eventually settle to the bottom, but might immediately appear by turning the clear solution cloudy.

Homework HW: Read Physical Changes on pg# 42 & Chemical Changes pg# Do 2.4 Section Assessment pg# 55 Answer question # Write out the question and answer for credit.

Solutions 28. The composition of matter always changes during a chemical change. 29. a transfer of energy, change in color, the production of a gas, the formation of a precipitate 30. The mass of the products is always equal to the mass of the reactants.

Solutions 31. In a physical change, the chemical composition of a substance does not change. In a chemical change, the chemical composition of the reactants changes as one or more products form. 32. a. physicalb. physical c. chemicald. chemical 33. Mass is conserved in every physical change or chemical reaction g