Adapted from Mrs Hoevers Chapter 4 Orange

Adapted from Mrs. Hoevers’ Chapter 4 : Orange Notes Rev. 2

Law of Conservation of Mass matter cannot be created or destroyed Matter can only change forms. (Reactants = Products) EX: Think about classes in school, same # of students and teachers, they are just arranged different based on the period

Video Chemical Equations • Can be written in words Vinegar + Baking Soda HC 2 H 3 O 2 + Na. HCO 3 • Can be written using atomic symbols Sodium + Water + Carbon acetate dioxide Na. C 2 H 3 O 2 + H 2 O + CO 2

Chemical Equations • Chemical name vs. Common name – Many chemicals have common household names. – In chemical equations their chemical name is used. EX. (the reaction between baking soda and vinegar) Sodium hydrogen carbonate + acetic acid Sodium acetate + Water + Carbon Dioxide

Chemical Equations Coefficient: The big number in front. 2 H 2 + O 2 2 H 2 O Subscript: The little number attached to the back of the symbol. If there is NO subscript, then there is only one atom of that element in the compound.

How many Atoms in the Formula? 1. H 4 H– 4 2. H 2 O H– 2 O– 1 3. C 6 H 12 O 6 C– 6 H – 12 O– 6 4. 2 Fe 4 Fe - 8 5. 6 Na. Cl Na - 6 Cl - 6 6. 3 Fe 4 O 3 Fe - 12 O-9

Video Chemical Equations 2 H 2 + O 2 2 H 20 Reactants Produces Products (Reaction) (Stuff before the reaction) (Stuff after the reaction)

REACTANTS • “Ingredients” • What you start with • These exist before the chemical reaction begins • On the left side of the arrow

PRODUCT • The finished product • “End result” • The result of a chemical reaction • The new substance that is formed • On the right side of the arrow

Is the Equation Balanced? Lets try a few to see…

Step 1 Draw a line down below the arrow to separate the reactants from the products C + O 2 CO 2

Step 2 List the elements on each side of the equation C + O 2 C O CO 2 C O

Step 3 Figure out how many atoms of each element are present on each side of the equation (subscript only applies to symbol it is attached after, if there is a coefficient the number stops at the arrow or a plus sign) C + O 2 C -1 O -2

Step 4 See if the number of atoms of each element are equal on both sides of the equation. C + O 2 C -1 O -2 CO 2 C -1 O -2

Example 2 2 H 2 O 2 H 2 + O 2 H -4 O -2

Now you try: 1. C + O 2 CO 2 2. H 2 + O 2 H 2 O 3. 2 H 2 O 2 H 2 + O 2 4. CH 4 + O 2 CO 2 + H 2 O 5. CH 4 + 2 O 2 CO 2 + 2 H 2 O 6. 3 Fe 2 O 3 + CO 2 Fe 3 O 4 + CO 2

Now you try: 1. C + O 2 CO 2 2. H 2 + O 2 H 2 O 3. 2 H 2 O 2 H 2 + O 2 4. CH 4 + O 2 CO 2 + H 2 O 5. CH 4 + 2 O 2 CO 2 + 2 H 2 O 6. 3 Fe 2 O 3 + CO 2 Fe 3 O 4 + CO 2

Now that you can tell whether or not an equation is balanced, lets try balancing a few. http: //www. wfu. edu/~ylwong/balanceeq/balanceq. html

Balancing Act Atoms are not CREATED or DESTROYED during a chemical reaction. Scientists know that there must be the SAME number of atoms on each SIDE of the EQUATION. To balance the chemical equation, you must add COEFFICIENTS in front of the chemical formulas in the equation. You cannot ADD or CHANGE subscripts!

Balancing Equations Step 1: determine the number of atoms for each element. Step 2: pick an element that is not equal on both sides of the equation. Step 3: add a coefficient in front of the formula with that element and adjust your counts. Step 4: continue adding coefficients to get the same number of atoms of each element on each side.

Balancing Equations

Balancing Equations Challenge Yields Reactants Products 2 Mg + O 2 2 Mg. O Subscript Coefficient Word Bank: Coefficient, Products, Reactants, Subscript, Yields

We must supply energy to break bonds.

Chemical Reactions and Energy • Chemical reactions always involve energy changes. • Making and breaking bonds involves energy changes

Energy in Chemical Reactions Endothermic Reaction: reaction that absorbs energy (endo – go in) Feels cold Exothermic Reaction: reaction that releases energy in the form of heat (exo- go out) Feels hot

• Breaking bonds requires energy. It is endothermic. • Making new bonds gives out energy. It is exothermic.

Activation Energy The amount of energy needed to break the bonds on the reactant side of a chemical equation

Chemical Reactions Thermal Energy & Heat Thermal energy: total energy of the particles in a sample of matter. Particles in matter are in constant motion. The amount of motion depends on the kinetic energy they possess. More kinetic energy=more motion. Hot matter has more kinetic energy than cold matter!

Kinetic energy = temperature! The more motion = higher temperature Think about when you work out or are active. The more you move the hotter you get.

Movement of Thermal Energy • Heat: the movement of thermal energy from a substance at a higher temperature to one at a lower temperature. Object Heat Cold Object

Rate of Reaction Video Tells how fast or slow (speed) a reaction occurs Things that will change the rate of reaction: 1. Temperature 2. Size of reactants – Surface Area 3. Concentration of reactant (how much)

Slow Down Reactions (Inhibitor) Inhibitor: doesn’t stop a reaction, but makes formation of certain products take longer EX: Adding lime juice to guacamole to keep it from turning brown, Refrigerators, Preservatives in foods

Speed Up Reactions (Catalyst) • Catalyst: It doesn’t change the products in a chemical reaction, it just speeds up the rate of reaction • Think “catapult” EX: enzymes in the body to speed up digestion, heat, oven, microwave

Section 1 Review 1. Are the following chemical equations balanced? Why or why not? a. Ca + Cl 2 Ca. Cl 2 b. Zn + Ag 2 S Zn. S + Ag c. Cl 2 + Na. Br Na. Cl 2 + Br 2. What evidence might tell you that a chemical reaction has occurred? 3. What is the difference between an exothermic and an endothermic reaction? 4. What forms of energy might be needed for a chemical reaction to take place?

Extras • http: //funbasedlearning. com/ (balancing equations) • http: //members. aol. com/profchm/balance. html Practice problems • http: //misterguch. brinkster. net/eqnbalance. html Step directions and examples for bal equations • http: //www. wfu. edu/~ylwong/balanceeq/balanceq. html Step by step interactive on bal equations (black board) • http: //www. middleschoolscience. com/balance. html (bal equations lab) • http: //www. sciencehouse. org/learn/Countertop. Chem/index. html demonstrations and labs using inexpensive everyday items • http: //www. middleschoolscience. com/index. html everything