Physical and Chemical Changes and Exothermic and Endothermic Reactions.
-
Upload
donald-ryan -
Category
Documents
-
view
305 -
download
1
Transcript of Physical and Chemical Changes and Exothermic and Endothermic Reactions.
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