Comparing Changes Physical Change Alters the form or appearance of matter Substance remains the same after the change Examples change in state slg bending crushing chopping ID: 419590
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Slide1
Physical vs. Chemical ChangesSlide2
Comparing Changes
Physical Change
Alters the form or appearance of matter.
Substance
remains the same after the changeExamples: change in state (s-l-g), bending, crushing, chopping.
Chemical Change
A reaction that produces
a new substance
with different properties than the original.
Ex
: combustion, electrolysis, oxidation, tarnishing.
Ex
: burning: when wood burns, elements in the wood combine with oxygen to form ash, CO
2
.Slide3
Examples of
Chemical Changes
Combustion: rapid combination of a fuel with
oxygen
Electrolysis: using electricity to break a compound into simpler compounds or elementsOxidation: Slow combination of a substance with oxygenTarnishing: Slow combination of a bright metal with sulfur, producing a dark coating on the metal.Slide4Slide5Slide6Slide7Slide8
Matter and Thermal Energy
Question: What is energy?
Energy
is the ability to
do work or cause change. Every change in matter includes a change in energy. burning a match: releases energy
melting ice:
absorbs
energy
Question: What is the difference between temperature and thermal energy?
Temperature
is the measure of the average energy of random motion of the particles of matter.
Thermal energy
– is the
total energy
of all the particles in an object. It always flows from
warmer
matter to
cooler
matter
.Slide9
Law of Conservation of Mass
In the late 1700’s,
French scientist Antoine Lavoisier performed experiments where he was able to measure the mass before and after a chemical change.
He discovered that
no mass was or gained in any reaction. The Law: Matter is neither created nor destroyed in any chemical or physical change.Slide10
Thermal Energy vs. Temp
Question 1
:
If you remove a cup of water from the ocean, does the water have the same temperature as the ocean?
Answer: Yes!Question 2: Do both have the same thermal energy?Answer: No. The ocean has much more thermal energy than the cup of ocean water because the ocean has much more mass.Slide11
An Ice Cube?
So, looking at the following two scenarios, describe the
transfer of thermal energy
. Which way is the thermal energy flowing?:
1. An ice cube melting on a counter top Thermal energy flows from the counter top and surrounding air (warmer) to the ice cube (cooler), causing it to melt.2. Ice cubes that are placed into a room-temperature sodaThermal energy flows from the soda (warmer) to the ice cubes (cooler), causing
the ice to melt and the soda to get cooler. So technically, the ice cubes don’t transfer “cold” to the soda, but instead the soda “heats” the ice.Slide12
Endothermic vs. Exothermic C
hange
When matter changes, it can either be:
Endothermic:
absorbing energyExamples: an ice cube melting, photosynthesisExothermic: releasing energy
Examples
:
a burning match, a fire,
the sunSlide13