chapter 1 matter, energy, and heat basics. 2 matter any substance that has weight, mass, and...

Chapter 1

Matter, Energy, and Heat Basics

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Matter

• Any substance that has weight, mass, and occupies space.

• Called an element when in the form of only one of the naturally occurring substances.

• The atom:– Smallest particle of an element– Also considered to be matter

• Can exist in any one of three physical states:– Solid, liquid, or gas

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Solids

• A substance that has definite volume and sufficient mechanical strength.

• Exert all their forces in the downward direction toward either the surface on which they are resting or toward the earth.

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Solids

• A block of ice. • A piece of wood.

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Liquids

• Liquids have definite volumes, but do not have definite shapes.

• The shape a liquid takes depends on the shape of the container that holds it.

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Gases• Gases have neither definite volume nor definite

shape.

• Gas molecules have little attraction for each other; the gas will completely fill any vessel that contains it.

• A gas exerts pressure in all directions against the walls of the container that holds it.

• Gas laws determine the behavior of contained gases.– Boyle’s Law– Charles’ Law– Dalton’s Law

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Gases

Gas molecules exert pressure on the walls of a balloon.

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Boyle’s Law

• States that there is a definite relationship between the pressure and volume of a gas if the temperature is kept constant.

• States that the pressure and volume of a gas are inversely related:– If the volume is decreased, the pressure will

increase– If the volume is increased, the pressure will

decrease

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Charles’ Law

• States that there is a definite relationship between the volume and temperature of a gas if the pressure is kept constant:– If the volume increases, the temperature increases– If the volume decreases, the temperature decreases

• States that there is a definite relationship between the pressure and temperature of a gas if the volume is kept constant:– If the pressure increases, the temperature increases– If the pressure decreases, the temperature decreases

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Dalton’s Law

• States that the total pressure of a confined mixture of different gases is equal to the sum of the pressures of each gas in the mixture.

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Dalton’s Law

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First Law of Thermodynamics

• States that energy cannot be created or destroyed, but can be converted from one form to another.

• Simply stated, when one form of energy is generated, it is done so at the expense of another energy form.

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Second Law of Thermodynamics

• States that energy tends to degrade into low-level heat energy.

• Heat energy is a byproduct of energy conversion and flows from a warmer substance to a cooler substance.

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Work

• Work is defined as the force exerted times the distance an object is moved.

• Work occurs when a force moves a mass a certain distance:– If no movement results, no work is being done

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Work

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Power

• Power is the rate of doing work, which is the amount of work per unit time.

• The term horsepower (hp) is used to measure units of power:– During the 18th century, it was determined that

a horse could lift 33,000 pounds to a height of 1 foot in one minute

– Lifting 33,000 pounds to a height of 1 foot in 30 seconds would therefore be equal to 2 horsepower

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British Thermal Units

• Heat content is measured in British thermal units (Btu):– The Btu is defined as the amount of heat

required to raise one pound of water 1 degree Fahrenheit

– Raising the temperature of one pound of water from 68°F to 70°F would therefore require 2 Btu of heat energy

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British Thermal Units

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Temperature Scales

• On the Fahrenheit temperature scale, water boils at 212 degrees and freezes at 32 degrees.

• On the Celsius temperature scale, water boils at 100 degrees and freezes at 0 degrees.

• Absolute zero, the temperature at which all molecular movement stops, is –460°F or –273°C

• On the Rankine and Kelvin scales, absolute zero is at 0 degrees (–460°F).

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Temperature Scales

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Conduction

• The heat transfers from one molecule to another within the substance.

• Metallic substances conduct heat better than nonmetallic substances.

• Good conductors of heat are typically good conductors of electricity.

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Conduction

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Convection

• Convection is the transfer of heat by a flowing medium.

• Heat transfer by convection takes place in liquids and gases, typically water and air.

• The process of convection can be sped up by using fans or pumps.

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Convection

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Radiation

• Heat that moves in the form of straight rays:– These rays produce heat when they come in

contact with a surface without heating anything in their path

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Radiation

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Sensible Heat

• Heat transfers that can be sensed with a thermometer:– Changing the temperature of air from 78°F to

72°F– Changing the temperature of water from 70°F

to 75°F– Changing the temperature of steam from

220°F to 230°F• The state of the substance remains

unchanged.

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Latent Heat

• In this process, heat is known to be added, but no temperature rise is measured.

• It results in a change of state with no change in temperature:– Changing ice at 32°F to water at 32°F– Changing water at 212°F to steam at 212°F

• Latent heat transfers cannot be measured with a thermometer.

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Latent Heat

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Pressure

• The force that is exerted on the walls of a vessel.

• Measured in force per unit area:– Atmospheric pressure is 14.7 pounds per square inch– Gauge pressure (PSIG) reads 0 psi at atmospheric

pressure– Absolute pressure (PSIA) reads 14.7 at atmospheric

pressure– Vacuum pressure is a reading below atmospheric

pressure