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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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A tale of two types
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


The law of conservation of energy
The Law of Conservation of Energy

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

  • Energy is the ability to do work or produce heat


Specific heat c
Specific Heat (c)

  • 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)


Specific heat continued
Specific Heat continued

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


Practice
Practice

  • 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


Vocabulary
Vocabulary

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


Types of reactions
Types of Reactions

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


In order for a reaction to proceed it must overcome the AE

Heat of Products

Heat of reaction

Heat of Reactants


Exothermic

  • 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


What type of reaction is this
What type of reaction is this:

Endothermic

DH is positive



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