Section 10.1 Energy, Temperature, and Heat Thermochemistry.

Section 10.1

Energy, Temperature, and Heat

Thermochemistry

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1. To understand the importance and general properties of energy

2. To understand the concepts of temperature and heat

3. To understand the direction of energy flow as heat

Objectives

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What is Energy?

Kinetic, potential, thermal, gravitational, sound, elastic, light / electromagnetic, electrical, electrostatic energies are examples

Energy is the driver of all changes. It flows between objects, it spreads out throughout the universe and in doing so is the driver of all observable phenomena (including chemical reactions)

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• Energy is the ability to do work or produce heat.

A. The Nature of Energy

Crane Lifting

Doing Work:

Explosion

Producing Heat:

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What is the difference between potential and kinetic energy?

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• Energy is the ability to do work or produce heat.

Potential energy

Energy of position

Kinetic energy

Energy of motion

E = ½ mv2


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• Law of conservation of energy

– Energy cannot be created or destroyed, only converted

Bounce Ball Into Space

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• Law of conservation of energy in a chemical reaction

– Energy can be converted from one form to another but can neither be created or destroyed.

– Stored chemical energy of reactants is equal to energy of products plus energy given off

– Some of the stored chemical energy of methane and oxygen is converted to heat as they react

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• Temperature is a measure of the random motions (kinetic energy) of the components of a substance.

B. Temperature and Heat

Hot water Cold water

(90. oC) (10. oC)

Fast Slow

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Measuring Temperature

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• Heat transfer is a flow of energy between two objects due to a temperature difference between the objects.– Heat transfer is the way in which thermal energy is

moved from a hot object to a colder object.

B. Temperature and Heat

Hot water Cold water

(90. oC) (10. oC)

Water Water

(50. oC) (50. oC)

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What is the difference between heat and temperature?

• Heat is the amount of thermal energy in an object because of its moving molecules.

• Temperature is a measure of thermal energy or how fast molecules are moving in an object. The more you heat something, the faster the molecules move. This is what causes temperature to rise.

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What is the difference between heat and temperature?• Heat and temperature are NOT the same thing. • Temperature is a measure of the average kinetic

energy of each particle within an object.• Thermal (heat) energy is the total energy of the

particles that make up an object• For example, there is a lot more heat inside a

glacier than in a pot of boiling water. The boiling water has a higher temperature, but the glacier has a lot more molecules. All the slower moving molecules in the large glacier equates to a higher thermal energy than the pot of hot water.

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Which picture shows the object that has more kinetic energy of particles?

Figure A Figure B

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Heat AnalogyParticles of hotter substances are

like the people in a “mosh pit…”

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…while particles of colder substances are more like the people at a tea party in a retirement home.

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Heat Transfer

The transition of thermal energy from a hotter to a cooler body

• Radiation• Conduction• Convection

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CONDUCTION

The transfer of heat energy between substances that are in

direct contact with each other.

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CONVECTIONOccurs when areas of a liquid or gas at different temperatures

rise and fall to due to density differences.

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RADIATIONDoes not rely upon any contact between the heat source and

heated material, as is the case with conduction and

convection.

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Measuring Heat

Calorie – Amount of heat required to raise the temperature of 1 gram of pure water by 1°C

The SI unit for energy and heat is the Joule (J) (1J = 0.2390 calories or 1 calorie = 4.184 J)

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Specific HeatSpecific heat of any substance is the amount of heat required to raise the temperature of 1 gram of that substance by 1°C.

For example, the specific heat of water is 4.184 J / g °C which this is the amount of energy that must be absorbed by each gram of water to rise it by one degree.

On the other hand, it only takes 0.129 J of energy to raise the temperature of an equal mass of gold by one degree.

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26

Examples of Specific Heats

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Specific Heat

The heat absorbed or released by a substance during a temperature change depends not only upon the specific heat of the substance, but also upon the mass of the substance and the amount by which the temperature changes.

Q = c x m x ΔT

Q = heat absorbed or releasedc = specific heat of substance (J / g °C)m = mass of the sample in gramsΔT = change in temperature in °C (Tfinal - Tinitial)

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C. Exothermic and Endothermic Processes

• System – part of the universe on which we focus attention• Surroundings – everything else in the universe

Look at the example of burning a match:

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C. Exothermic and Endothermic Processes

• Exothermic – heat energy flows out of the system

• Endothermic – heat energy flows into the system

Section 10.1 Energy, Temperature, and Heat Thermochemistry.

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Transcript of Section 10.1 Energy, Temperature, and Heat Thermochemistry.