The ability to do work The ability to transfer heat Two types: Kinetic and Potential.

The ability to do work The ability to transfer heat

Two types: Kinetic and Potential

Energy do to motion or action electromagnetic waves (light), heat,

motion, electrical current, A moving truck has the ability to

flatten you - do work on you!

Energy due to position (gravitational or electrical) or chemical bonds

Stored energy Position: boulder at the top of the hill,

water behind a dam, stick of plastique

Chemical: tank of gas, hamburger

• Death is very likely the single best invention of Life. It is Life's change agent. It clears out the old to make way for the new.

• Right now the new is you, but someday not too long from now, you will gradually become the old and be cleared away. Sorry to be so dramatic, but it is quite true. Your time is limited, so don't waste it living someone else's life.

• Don't be trapped by dogma — which is living with the results of other people's thinking. Don't let the noise of others' opinions drown out your own inner voice. And most important, have the courage to follow your heart and intuition.

• They somehow already know what you truly want to become. Everything else is secondary.

Energy can neither be created nor destroyed, but you may change from one form to another

When energy is changed from one form to another, some of the energy is degraded to a lower-quality, more dispersed energy form• No reaction can be 100% efficient• All reactions lose energy (usually as heat)• Systems only go spontaneously in the

direction of decreasing order (increasing entropy)

• heat always flows from hot to cold

Entropy is the amount of disorder in a system

Entropy always increases over time (in the absence of an input of outside energy)

example. cleaning up your room

There are two units which are commonly used:

Calories (c): amount of energy it takes to raise one gram of water one degree Celsius• Calories in food (C) = kilocalories(kcal) = 1000

calories Joules (J): 4.18 Joules = 1 calorie

Heat is the amount of kinetic energy of the atoms

Temperature measures the average speed of the atoms

Homework pages 8-9

J Deutsch 2003 20

•AIM•Heating and Cooling Curves

•DO NOW•Page 14

Exothermic - Potential energy decreases•Releases energyH, change in heat, is negative•Energy is on the right

2H2 + O2 2H2O + energy

Endothermic - Potential energy increases•Absorbs energyH, change in heat, is positive•Energy is on the left

2H2O + energy 2H2 + O2

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A hot pack contains chemicals that can be activated to produce heat. A cold pack contains chemicals that feel cold when activated.

1. Based on energy flow, state the type of chemical change that occurs in a hot pack.

Exothermic

2. A cold pack is placed on an injured leg. Indicate the direction of the flow of energy between the leg and the cold pack.

From the leg to the cold pack (Hot to Cold)

3. What is the Law of Conservation of Energy? Describe how the Law of Conservation of Energy applies to the chemical reaction that occurs in the hot pack.

Energy cannot be created nor destroyed. It can only be changed from one form to another. The heat produced in the hot pack was stored in the chemical bonds.

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Potential energy changes, so temperature doesn’t

Boiling Point

Melting Point

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AB•solid warms up (KE/PE constant)

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BC•solid melts (KE constant/PE)

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CD•liquid warms up (KE/PE constant)

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DE•liquid boils (KE constant/PE)

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DE•liquid boils (KE constant/PE)

EF•gas warms (KE/PE constant)

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As ice melts at standard pressure, its temperature remains at 0°C until it has completely melted. Its potential energy

(1) decreases

(2) increases

(3) remains the same

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A sample of water is heated from a liquid at 40°C to a gas at 110°C. The graph of the heating curve is shown in your answer booklet.

a On the heating curve diagram provided in your answer booklet, label each of the following regions:

Liquid, only Gas, only Phase change

Liquid Only

Gas OnlyPhase change

J Deutsch 2003 40

b For section QR of the graph, state what is happening to the water molecules as heat is added.

c For section RS of the graph, state what is happening to the water molecules as heat is added.

They move faster, their temperature increases.

Their intermolecular bonds are breaking, their potential energy is increasing.

J Deutsch 2003 41

What is the melting point of this substance?

(1) 30°C (3) 90°C

(2) 55°C (4) 120°C

How do we calculate amount of heat,(Q), if we are not given a graphic?

Q = mCT Q = mHf Q = mHv Have to figure out which one to

use for a given problem. Depends which section of

heating curve. Look for hints in the problem.

Calculating Heat Transferred

Q = mCT

Simple system: Pure substance in a single phase. To calculate heat gained or lost, use:

•Q = amount of heat transferredQ = amount of heat transferred•m = mass of substancem = mass of substance•C = specific heat capacity of the substance C = specific heat capacity of the substance (Table B).(Table B).•T = temperature change = TT = temperature change = Tfinalfinal – T – Tinitialinitial

Temperature changed

Temperature increased

Temperature decreased

Initial / Start temperature

Final temperature

Ending temperature

From ____ to ____ Water

Amount of energy required to convert 1 gram of a pure

substance from the solid to the liquid phase at the melting point.

Heat of Fusion

Q = mHf

Use this equation to calculate energy changes for phase changes between ice & liquid water at 0C.

Ice Freezing Melting At 0C (for H2O) At constant temperature

Amount of energy required to convert 1 gram of a pure

substance from the liquid to the gas phase at the boiling point.

Heat of Vaporization

Q = mHv

Use this equation to calculate energy changes for phase changes between steam & liquid water at 100C.

Steam Boiling Condensation At 100C (for H2O) At constant temperature

The ability to do work The ability to transfer heat Two types: Kinetic and Potential.

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