Physical and Chemical Changes

andExothermic and

Endothermic Reactions

Physical Change

● Changes in a substance that do not alter the chemical properties of the substance

● Things about the substance change, but the substance remains the same

● For instance, an ice cube melts into water and you can boil that into a gas, but it remains H2O the whole time

● One or more of its physical properties may be changed

● Ex: change in size, shape, dissolving. possibly color change (as long as a new substance is not created)

Chemical Change

●Changes that alter the chemical

properties of a substance

●A change that creates a different

substance

●Clues: bubbles (indicates the

production of a gas), getting hot or

cold, color change

●Ex: iron rusting, souring of milk,

burning paper

Endothermic and exothermic reactions

Step 1: Energy must be SUPPLIED to break chemical bonds:

Step 2: Energy is RELEASED when new chemical bonds are made:A reaction is EXOTHERMIC if more energy is RELEASED than SUPPLIED. If more energy

is SUPPLIED than is RELEASED then the reaction is ENDOTHERMIC

Endothermic Reactions:

a change (e.g. a chemical reaction) that requires (or

absorbs) heat.Photosynthesis is an endothermic reaction

(requires energy input from sun)

Forming Na+ and Cl- ions from NaCl is

an endothermic

process

Measuring Heat

reaction

Endothermic reaction = heat

taken in & temperature of the substance

drops

Ammonium nitrate + water

Starting temperature 20 C⁰

Add ammonium nitrate to water

ending temperature of 12⁰ Ca temperature decrease of 8 C⁰

Activation energy

Energy given out

by reaction

Exothermic Reaction: a change (e.g. a chemical

reaction) that releases heat.

Burning fossil fuels is an exothermic

reaction

Heat Released

Exothermic reaction =

heat given off & temperature of substance

rises.

reaction

Exothermic vs endothermic:

EXOTHERMIC – more energy is given out than is taken in (e.g. burning, respiration)

ENDOTHERMIC – energy is taken in but not necessarily given out (e.g. photosynthesis)© Teachable . Some rights reserved. http://teachable.net/res.asp?r=1910

Examples

Exothermic

• Combustion of fuels

• Evaporation of Water

• Yeast & Hydrogen Peroxide

• Epsom salts & water

Endothermic

• Photosynthesis• Acetic Acid &

Sodium Bicarbonate

• Cold Packs• Melting Ice

© Teachable . Some rights reserved. http://teachable.net/res.asp?r=1910

1. Zinc turnings are placed in a hydrochloric acid solution

2. Ripping Magnesium ribbon into pieces then ignited in a flame

3. A penny is coated with zinc then heated

Normal Penny

Coated with Zinc

After being heated

4. Polymers A and B are mixed

5. Hexane is poured down ramp and ignited

6. A styrofoam cup in acetone

7. Gas bubbles are made, then ignited