CHAPTER SEVEN Chemical Reactions

Section 1: Chemical Formulas and Equations  Matter can undergo two kinds of changes:  Physical change Affect its physical properties such as size, shape or its state of matter. Example: water frozen to ice Physical or Chemical Change?

Section 1: Chemical Formulas and Equations  Matter can undergo two kinds of changes:  Chemical change Results in the formation of a new substance that has different properties from the original substance Example: rust on a car, egg is fried, leaves turn colors, etc. A process that produces chemical change is a chemical reaction. Physical or Chemical Change?

Section 1: Chemical Formulas and Equations  Can anything go through both changes?  Yes! Example: Newspaper… crumple it up, after a long time it changes color, and then you could burn it! Physical or Chemical Change?

Section 1: Chemical Formulas and Equations  A chemical equation describes what happens in a chemical reaction.  The chemical equation identifies: Reactants (starting materials) Products (resulting substance) The formulas of the participants The phases of the participants (solid, liquid, gas) The amount of each substance. Chemical Equations

Section 1: Chemical Formulas and Equations  Balancing a chemical equation refers to establishing the mathematical relationship between the quantity of reactants and products. Chemical Equations

Section 1: Chemical Formulas and Equations  Steps to Balancing a Chemical Equation  C 3 H 8 + O 2  CO 2 + H 2 O Write the unbalanced equation. Count the number of atoms in each side (reactants and products) element by element. Balancing Chemical Equations

Section 1: Chemical Formulas and Equations  Steps to Balancing a Chemical Equation  C 3 H 8 + O 2  CO 2 + H 2 O Start with an element found in one compound on each side of the equation. Change the coefficients (#’s in front of the compound) so that the number of atoms of the element is the same on each side of the equation. Repeat with all other elements in the chemical equation. Check your work. Balancing Chemical Equations C 3 H 8 + 5O 2  3CO 2 + 4H 2 O

Section 1: Chemical Formulas and Equations  Try these 3 equations on your own…  Ag + H 2 S  Ag 2 S + H 2  Na + AlCl 3  NaCl + Al  H 2 O 2  H 2 O + O 2 Balancing Chemical Equations

Section 1: Chemical Formulas and Equations  Two kinds of reactions:  If energy is absorbed, this is called an endothermic reaction. (cools down)  If energy is released, this is called an exothermic reaction. (heats up) Energy in Chemical Reactions

Section 1: Chemical Formulas and Equations  REMEMBER:  Energy is not created or destroyed, it just changes form.  When bonds are broken, or changed, energy is involved.  Some bonds are broken, while others are formed.  Therefore, there will always be a change in energy.  Energy will either be released, or absorbed, during a chemical reaction. Energy in Chemical Reactions

Section 2: Rates of Chemical Reactions  To form new bonds in the product, old bonds must break in the reactants, and breaking bonds takes energy.  To start any chemical reaction, a minimum amount of energy is needed and this energy is called activation energy. Activation Energy – Starting a Reaction

Section 2: Rates of Chemical Reactions  A rate tells you how much something changes over a given period of time.  For example, rate of speed.  The rate of reaction tells how fast a reaction occurs after it has started.  To find the rate of reaction, you can measure either how quickly one of the reactants is consumed or how quickly one of the products is created. Reaction Rates

Section 2: Rates of Chemical Reactions  Conditions that affect rate:  Temperature: changes the atom and molecule speed.  Concentration: the amount of substance present in a certain volume. Reaction Rates

Section 2: Rates of Chemical Reactions  Inhibitor: a substance that slows down a chemical reaction.  Catalyst: a substance that speeds up a chemical reaction  An enzyme is a large protein molecule that speeds up reactions needed for your cells to work properly. Speeding Up and Slowing Down Reactions

Make a list of Physical & Chemical Changes  Physical Changes:  Melting of ice  Drying of wet clothes  List 6 more physical changes  Draw a picture for 4 of them…  Chemical Changes:  Rusting of iron  Darkening of apples  List 6 more chemical changes  Draw a picture for 4 of them…

Chapter Reviews!!!  Pg. 184 #1-20  Pg. 212 #1-21