Chemistry—Chapter 2

ENERGY

What is ENERGY?(list types of energy)

• The ability to do WORK.

What is WORK?

• The ability to move something, create a new compound or generate light.

Law of Conservation of Energy

• Energy is neither Created nor Destroyed.

• Energy isn’t really lost or gained—it is TRANSFERRED to the System and its Surroundings.

What is the System?What is the Surroundings?Where is the energy transfer?

Transfer of Energy

• http://www.youtube.com/watch?v=s-KvoVzukHo

• Movement of the molecules requires energy. So which state requires the most energy?

Every Change in Matter Requires a Change in Energy

Chemical Changes

• Remember that changes of state are PHYSICAL changes, while CHEMICAL changes actually change the substance.

• In order for a CHEMICAL change to occur, there must be CONSERVATION of ENERGY.

• THE LAW of CONSERVATION of ENERGY states that “ENERGY is neither CREATED nor DESTROYED”.

Conservation of ENERGY

• When a Physical change happens, for example, a Phase change, energy is either absorbed or released.

• The same is true for a Chemical change.– If energy is released it is EXOTHERMIC– If energy is absorbed it is ENDOTHERMIC• EXOTHERMIC—gets hot!• ENDOTHERMIC—gets cold!

Remember to look at the SYSTEM and its SURROUNDINGS

• For example, when RUST happens (oxygen combines with iron), this is an Exothermic process, but if you walk outside and touch something rusty it doesn’t feel warm. WHY?

Why?

• The heat is given off to the ATMOSPHERE (the surroundings).

• It is very hard to detect a tiny increase in HEAT in a giant atmosphere.

• Its like adding a teaspoon of salt to a cup of water or an ocean. Would you detect the salt increase in the ocean?

One type of ENERGY is HEAT

• Heat is energy transferred from one object to another which makes molecules move.

• Heat always moves from a HOT object to a Cooler one. One cannot transfer COOLness.– Why do icecubes in a glass of water melt?

Exothermic Reactions

• Explosions are Rapid Releases of Heat. • Energy can be stored (potential energy) as

CHEMICAL ENERGY and released during a reaction as KINETIC ENERGY.

http://www.youtube.com/watch?v=GyVD8V0016w

Exothermic Reaction

Endothermic Reactions

• Ice Packs that get cold when you break them are ENDOTHERMIC—they absorb heat when a reaction inside the bag occurs.

Endothermic Reaction

http://www.youtube.com/watch?v=YL-uS7kMa0I

HEAT IS DIFFERENT than TEMPERATURE!!

• Temperature is the AVERAGE energy of molecules in a substance. Some molecules will have more energy and others less, but the AVERAGE is the temperature.

Changes of State

solid

liquid

gas

TEM

PERA

TURE

HEAT

What is KELVIN ?

Farhenheit Celsius Kelvin

- 459 -273 0

32 0 273

212 100 373Water Boils

Ice Melts

“Absolute 0”

How to calculate Kelvin/Celsius

• Every degree Celsius can be converted to Kelvin by ADDING 273.– Example: 0 Celsius = 273 Kelvin

• Every degree Kelvin can be converted to Celsius by SUBTRACTING 273.– Example: 373 Kelvin = 100 Celsius