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# Energy - PowerPoint PPT Presentation

Energy. L. A tale of two types. Exothermic. Potential Energy. Kinetic Energy. Energy of motion Measurement of Temperature °C – relative K - actual. Endothermic. Stored energy Based on composition or location Measured with: Measured in: Calories (cal) Joules (J). L.

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## PowerPoint Slideshow about ' Energy' - loe

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Presentation Transcript

### Energy

L

Exothermic

Potential Energy

Kinetic Energy

Energy of motion

Measurement of Temperature

°C – relative

K - actual

Endothermic

• Stored energy

• Based on composition or location

• Measured with:

• Measured in:

• Calories (cal)

• Joules (J)

L

• Energy can neither be created nor destroyed, it can only change forms

• Energy is the ability to do work or produce heat

• The amount of energy to raise 1g of a substance by 1°C

• Unique to a substance

q = mcDT

q = heat (J or cal)

m = mass (g)

c = specific heat (J/(g°C) –or-- cal/(g°C))

DT = change in temperature (°C)

The temperature of a sample of iron with a mass of 10.0g changed from 50.4°C to 25.0°C with the release of 114 J heat. What is the specific heat of iron?

q = mcDT

114 J = 10.0g (c) (50.4°C – 25.0°C)

114 J = 254 g°C (c)

0.449 j/g °C

• If the temperature of 34.4g of ethanol increases from 25.0°C to 78.8°C how much heat will be absorbed by ethanol? (cethanol = 2.44 j/g°C)

• A 4.50g nugget of pure gold absorbed 276J of heat. What was the final temperature of the gold if the initial temperature was 25.0°C? (cgold = 0.129J/g°C)

• 4520 J

• 500 °C

If this is a reaction “you are part of the system”

• System – where the reaction is taking place and the elements involved

• Surrounding – everything not the system

Endothermic

Exothermic

Releases energy

System heat decreases

Surrounding heat increases

Bond formation is always exothermic

Therefore energy is a product

Conversion of PE to KE

• Absorbs energy

• System heat increases

• Surrounding heat decreases

• Bond breaking is always endothermic

• Therefore energy is a reactant

• Conversion of KE to PE

Heat of Products

Heat of reaction

Heat of Reactants

• ΔHreaction = Hproducts - Hreactants

• H = heat (J)

• ΔH is the change in the heat of the system under constant pressure.

• Exothermic: –ΔH.

• Makes kinetic energy

• Endothermic: +ΔH.

• Uses kinetic energy

Endothermic

• Potential Energy

• Kinetic Energy

Endothermic

DH is positive