CH. 1 CHEMICAL REACTIONS

Chemistry

The study of matter and how it changes

-Matter is anything that has mass and takes up space.

Building Blocks of Matter

Elements: A substance that cannot be broken down into any other substance by chemical or physical means. Ex: H, Na, Cl. An atom is the smallest piece of an element.

Compounds: Two or more elements chemically combined. Ex: H2O, NaCl. Molecules are the smallest pieces of compounds.

Mixture: Elements and compounds in the same place but not combined into a new material.

Ex: Soil, Salt water, Salad

Activity

Students will read and perform activities 2 and 3 in the Periodic Table packet.

Need: Colored pencils located in the bottom drawer of the front beige filing cabinet.

If there’s not enough blue, green and yellow, choose different colors as long as they’re not too dark to see the information beneath.

Changes in Matter

Physical Change: A change in size (cut it in half), shape (pound it into a sheet) or state (turn from solid to liquid or gas.)

Chemical Change: A change in matter that produces new substances.

Ex. Burning, oxidation, carbonation

Recognizing the Difference

In a chemical change new substances with different characteristics form. Physical changes leave the material the same as it was.

Chemical reactions occur when bonds between elements in a compound are formed or broken apart.

Homework

Page 21, questions 1-5. Use proper heading that is found on the wall near the clock.

Describing Chemical Reactions

Chemical equations-use symbols instead of words.

First: Chemical compounds are listed as chemical formulas, like: H2O, NaCl, HCl

Second: They are arranged with the reactants on the left and the products on the right like this:

Reactants Products

The arrow means: reacts to yield. Which means MAKES!

Example:Reactants Products (Remember) 2 H2 + O2 2 H2O

These small numbers are called subscripts. They tell you how many of a certain element are in a molecule.

Reactants Products (Remember) 2 H2 + O2 2 H2O

The big number is called a coefficient. It tells you how many molecules of a substance there are in a chemical reaction.

The Principle of Conservation of Mass

When a chemical reaction occurs, the mass of reactants before the reaction will equal the mass of the products after the reaction.

This principle may not always appear to be true. The mass of wood before a fire does not equal the mass of the ash after the fire. In this case some of the mass was in the gases emitted by the burning of the wood: CO2, H2O etc.

The need to balance chemical equations.

An equation needs to follow the Principle of Conservation of Mass.

Example: ___H2 + ___O2 ____H2O

-We put in coefficients to balance the equation.

-Use a T chart! See next slide.

Balancing Example

___H2 + ___O2 ____H2O Reactants ProductsH 2 2O 2 1

You can see the atoms don’t match on the reactant and product side. We will use coefficients to fix this. See next slide.

Balancing Example

___H2 + ___O2 ____H2O Reactants ProductsH 2 4 2 4O 2 1 2

By placing a 2 in the blanks of the equation we balance the elements on both sides of the equation which makes it follow the Law of Conservation of Mass.

2 2

Classifying Chemical Reactions

Synthesis: The reactants make a product.

2H2 + O2 2 H2O

Synthesis reactions have plus sign(s) on the left.

Classifying Continued:

Decomposition: The reactant is broken into 2 or more products.

2H2O 2H2 + O2

The Last on Classification:

Displacement: When one or more elements change partners in the formulas involved in a chemical equation.

Example:HCl + NaOH NaCl + H2O

Switch your partner doh si doh!

Homework

Page 31, questions 1-5. Skip 4 if Mr. Lynch isn’t here.

Make sure to put our heading on your paper.

Energy in Chemical Reactions

Every Reaction involves a change of energy. Some reactions release energy and some absorb energy.

This makes for 2 types of reactions: Exothermic Reactions: Release energy in the form of heat and feel warm or hot to the touch. Endothermic Reactions: Absorb energy and feel cool or cold to the touch.

Exothermic Reactions. Examples:

4 Fe + 3 O2 -> 2 Fe2O3

This is what happens in a hand warmer. (Those packets you break open that get warm when iron is exposed to the oxygen in the air.)