Chapter 10

Chemical Reactions and Equations

Lesson 1: Understanding Chemical Reactions

Chemical Equation

Signs of a Chemical Change

Day 1

Review of what we already know

• Chemical reactions happen when two chemicals combine and create a NEW SUBSTANCE.

Na + Cl NaCl

• The law of conservation of mass states that the mass of the reactants is equal to the mass of the products.

Sample Chemical Reaction Equation

In most chemical reactions, two or more substances, called reactants, interact to create different substances called products.

REACTANTS go IN CHEMICAL REACTION PRODUCTS come OUT

• In a chemical reaction, only the atoms present in the reactants can end up in the products.

• NO NEW ATOMS are created OR destroyed. (Law of Conservation of Mass)

• In a chemical reaction, reactants contact each other, bonds between atoms in the reactants are broken, and atoms rearrange and form new bonds to make the products.

REACTANTS go IN CHEMICAL REACTION PRODUCTS come OUT

Reactants go IN Products come OUTCHEMICAL REACTION

Atoms Reactant Side Product Side

Carbon

Hydrogen

Osygen

LET’S PRACTICE TOGETHER

Reactants go IN Products come OUTCHEMICAL REACTION

ANSWER

Law of Conservation of Mass

The law of conservation of mass states that the mass of the reactants is EQUAL to the mass of the products.

Now you practice

More practice

Correct answers

• Both are balanced equations.

• Propane combustion includes 3 Carbon atoms, 8 Hydrogen atoms, and 10 Oxygen atoms.

• Butane combustion includes 8 Carbon atoms, 10 Hydrogen atoms, and 26 Oxygen atoms.

Lesson 1 Review1. What are the chemicals that go IN to a reaction

called?

2. What are the chemicals that come OUT of a reaction called?

3. Where do the atoms in the products of a chemical reaction come from?

4. Are atoms created or destroyed in a chemical reaction? Explain.

ANSWERS to Lesson 1 Review1. What are the chemicals that go IN to a reaction called? REACTANTS

2. What are the chemicals that come OUT of a reaction called? PRODUCTS

3. Where do the atoms in the products of a chemical reaction come from? The atoms in the product are atoms from the reactants that have been rearranged after the chemical bonds were broken.

4. Are atoms created or destroyed in a chemical reaction? Explain. Law of Conservation of Mass simplified . . . . . . Mass of reactants = mass of products

Lesson 3: Energy Changes and Chemical Reactions

Day 2

Review of what we know

• Endothermic chemical reactions absorb thermal energy. (feel cool or cold)

• Exothermic chemical reactions release thermal energy. (feel warm or hot)

Question to discuss

Which temperature do you think would speed up the rate that a chemical change happens, hot or cold? Justify your answer.

Why does temperature affect the rate of a chemical change?

• For a chemical change to occur the reactants must contact each other. This collision happens faster in warm or hot temperatures because more of the molecules are moving faster in warmer temperatures.

New Vocabulary to add to notebook

• Activation Energy: The amount of energy needed to begin a chemical reaction.

• Catalyst: A substance that increases the rate of the chemical reaction but does not become part of the products.

Design an experiment time Design an experiment to test the problem

question below.

• Problem: Does temperature affect the rate of chemical change in a glow stick?

• Hypothesis: If . . . . .then . . . . because• Variables:• Materials: 2 glow sticks, . . . . • Procedure:

Review of Scientific Method

Mrs. Shaw’s Experiment

• Problem: Does temperature affect the rate of chemical change in a glow stick?

• Hypothesis: If warm temperatures increase chemical reactions then the glow stick placed in warm water will shine brighter than the one in cold water because molecules will collide and produce a chemical reaction faster in warmer water.

• Materials: 2 glow sticks, 2 -250ml plastic beakers, water, ice, thermometer, . . . .

• Procedure: next slide

Mrs. Shaw’s Experiment

• Procedure:1. Get two 250 ml plastic beakers and fill with 200 ml tap water each.2. Place one of the beakers in the freezer and wait until temperature

reaches 25 degrees Celsius. 3. When beaker in freezer has reached desired temp. place the other

beaker in the microwave and heat until water temp is 60 degrees Celsius.

4. When both beakers have reached appropriate temp. place both on counter and break (activate) both glow stick.

5. Place one glow stick in each cup and document the observations and level of brightness that each glow stick gives off.

6. Repeat procedure 5 times.

Data and Results

• What did our data show when we did the experiment?

• Write a conclusion that explains what happened, what could have been a source of error, what we should do differently next time, and how this experiment could be extended.