Chemical Changes in Matter
I. Matter Properties---
A. States of matter – depends on temperature and pressure---four states of matter--solid, liquid, gas, plasma
B. Physical Properties – any characteristic of measured matter that can be observed
1. Length
2. Mass
3. Volume
4. Density--- the measure of the relative "heaviness" of objects with a constant volume
5. Melting point – temperature at which a solid becomes a liquid
6. Boiling Point – temperature at which a liquid becomes a gas
7. Metallic Properties – can include luster, malleability, and magnetism
C. Chemical Properties – Characteristics that give a substance the ability to undergo a change that results
in a new substance.
1. Flammability
2. Reactivity---reacts with oxygen, light, water, or other substances
II. Methods by which matter changes.
A. thermal expansion: tendency of matter to increase in volume or pressure when heated. (bridge span) Water is an exception—it decreases in volume as it goes from solid to liquid.
B. evaporation (vaporization): process by which molecules in a liquid state (e.g. water) spontaneously become gaseous (e.g. water vapor), without being heated to boiling point. (water to steam)
C. condensation: change in matter of a substance to a denser phase, such as a gas (or vapor) to a liquid. (steam to water droplets)
D. sublimation: solid changes directly to a gas without going through the liquid state (dry ice)
E. deposition: opposite of sublimation—gas to solid without going through the liquid stage (water vapor changes directly into ice: snowflakes or frost)
F. solubility: the extent to which a solute will dissolve in a solvent; a solute is the thing that is dissolved, whereas a solvent is what it is dissolved in; water is the universal solvent
III. Physical and Chemical Change
A. Physical Change – Changes the appearance of a substance but does not affect its chemical properties.
§ Examples: sharpening a pencil, cutting a piece of paper, ice melting, candle wax melting
B. Chemical Change – changes in the identity of a substance due to its chemical properties.
1. Signs of a chemical change---
· The formation of a gas, smoke, or bubbles
· An odor is given off
· A change in color
· The production of heat or light
· The formation of a solid
2. Chemical changes are not reversible using physical means.
§ Slow oxidation—rusting iron or wood rotting---occurs at ordinary temp; produces no light or noticeable heat
§ Fast oxidation—combustion, burning or explosion---occurs rapidly; burning of a material; produces light and noticeable heat
§ Food spoilage—oxidation process or enzyme action
o Meat and fruit contain enzymes that will cause the breakdown of tissues unless they are inactivated. Oxidation is caused by the oxygen in the air. When you cut up fruit for instance, the parts without skin which are exposed will turn brown quickly. Squeezing lemon juice over your fruit will stop oxidation because the juice contains Vitamin C (ascorbic acid). The ascorbic acid reacts with the oxygen preventing the browning on the fruit.
3. Energy is released or absorbed during a chemical reaction.
4. Endothermic reactions absorb heat energy. Example: Frying an egg---You must keep adding heat, or the reaction will stop.
5. Exothermic reactions release heat energy. Example: Burning wood---Heat is given off.
6. The rate of a chemical reaction can be influenced by the temperature, the concentration of reactants, and the exposed surface area of the reactant particles.
7. A substance that slows down a chemical reaction is called an inhibitor. (stop the spoiling of foods)
8. A catalyst is a substance that speeds up a chemical reaction.
9. Activation energy---energy needed to get a reaction started
9. Some of the most effective catalysts are at work in thousands of reactions that take place in your body. These catalysts, called enzymes (biological catalyst), are large protein molecules that speed up reactions needed for your cells to work properly.
10. The Law of Conservation of Mass by Antoine Lavoisier----matter cannot be created or destroyed
