Book L, Chemical Interactions
Chapter 1, Chemical Reactions

Section 1, Matter and its changes

Chemical changes

How can you tell (if it is a chemical change)?

1. color change -- this is not just paint or food coloring

example:

- an a base (cloudy liquid) added to an acid (clear liquid) with an indicator produces a pink liquid

- fireworks

2. precipitation - the formation of a solid from two liquids (no this is different from rain!)

example:

limewater (a cloudy liquid) added to cobalt chloride (a red liquid) produces cobalt hydroxide (a blue solid) 

3. gas production

example: Baking soda and vinegar react to make the gas carbon dioxide

another example: peroxide (clear liquid) added to potassium iodide ( a white solid) produces oxygen (a gas)

4. Changes in temperature

-some chemical changes release heat energy -- they get hotter and are called exothermic

example:

 calcium chloride added to water produces (releases) heat energy (the beaker feels hotter)

-some chemical changes absorb heat energy -- they get colder and are called endothermic

example:

sodium bicarbonate added to acetic acid absorbs heat energy (the beaker feels colder)

5. Changes in properties

example:

Bread dough becomes bread.

Name two differences in the properties of bread compared to bread dough

Physical changes -- never produce a new substance

How can you tell (if it is a physical change)?

 1. color change-- produced by a dye or paint

example: painting a wall, putting food coloring in frosting

2. phase change -- example: boiling or freezing water

3. making a mixture -- example: putting sand in water or making a milkshake

 Chemical changes (which occur when there is a chemical reaction) occur when chemical bonds are either formed or broken.

 Section 2, Describing chemical reactions

Elements are represented by chemical symbols

Compounds are represented by chemical formulas

one molecule of the compound water = H^₂O

A subscript shows the number of atoms of an element in each molecule of a compound

(note: if there is no subscript it is assumed to be a one)

Note to students copying this from the web site: Please do not just copy the answers in the next section. Come to me for help if you have missed this lesson. It is important the you understand this information. It is not just vocabulary. Please make an appointment to see me after school. In fact, you can email me right now. Go back to my home page and click on the email button.

Mrs. McIntosh

examples:

- one molecule of H₂O₂ has two atoms of hydrogen and two atoms of oxygen

- one molecule of CO₂ has one atom of carbon and two atoms of oxygen

- one molecule of CO has one atom of carbon and one atom of oxygen

- one molecule of C₃H₈ has three atoms of carbon and eight atoms of hydrogen

- one molecule of C₆H₁₂O₆ has six atoms of carbon, twelve atoms of hydrogen, and six atoms of oxygen

- one molecule of Na₂CO₃ has two atoms of sodium, one atom of carbon, and three atoms of oxygen

- one molecule of Al₂O₃ has two atoms of aluminum and three atoms of oxygen.

Chemical equations are used to show chemical reactions.

Fe + S ------------> FeS

one atom of iron + one atom of sulfur produce one molecule of Fe S

reactants ------------> products

The arrow is read "produce". Reactants produce products.

Conservation of mass

- the amount of matter in a chemical reaction does not change so .........

The total mass of the reactants must equal the total mass of the products.

This leads us to ...........

Balancing chemical equations

- Chemical equations must show that the mass of the reactants equals the mass of the products

example:

HF = one molecule of the compound HF (hydrogen fluoride) which contains one atom of the element H (hydrogen) and one atomof the element F (fluorine).

2HF = two molecules of the compound HF which each contain one atom of the element H (hydrogen) and one atom of the element F (fluorine). There is a total of two atoms of hydrogen and two atoms of fluorine.

Practice coeficients:

2 C₂H₄ = two molecules of C₂H₄ = a total of four atoms of C and eight atoms of H

5 C₂H₄ = five molecules of C₂H₄= a total of ten atoms of C and twenty atoms of H

3 C₆H₁₂O₆ = three molecules of C₆H₁₂O₆ = a total of eighteen atoms of C and thirty six atoms of H, eighteen atoms of O

5C₆H₁₂O₆= five molecules of C₆H₁₂O₆= a total of thirty atoms of C and sixty atoms of H, and thirty atoms of O

Practice balancing equations:

Be sure to get help here.

Zn + HCl ---------------> ZnCl^₂ + H₂

answer:

Zn + 2HCl ---------------> ZnCl^₂ + H₂

See Mrs. McIntosh for more examples.

Section 3, Controlling chemical reactions

Energy is involved in every chemical reaction. Some chemical reactions release energy and some chemical reactions absorb energy.

Exothermic reactions release heat energy.

Endothermic reactions absorb heat energy.

Other chemical reactions may involve:

1. light energy

example: light stick

2. electrical energy

example: a battery

 3. mechanical energy

example: a piston in an engine

 Section 4: Fire and fire safety -- read on your own if interested