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# Thermal Energy

Thermal Energy. Kinetic Molecular Theory. All matter consists of atoms Molecules are ALWAYS in motion Molecules in motion possess kinetic energy Molecular motion is random Collisions between atoms and molecules are imminent! When molecules collide, energy is transferred between them

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## Thermal Energy

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1. Thermal Energy

2. Kinetic Molecular Theory • All matter consists of atoms • Molecules are ALWAYS in motion • Molecules in motion possess kinetic energy • Molecular motion is random • Collisions between atoms and molecules are imminent! • When molecules collide, energy is transferred between them • A collision is the only means of changing direction for a gas molecule • Thermal energy is the average of the potential and kinetic energies possessed by atoms and molecules experiencing random motion.

3. Phases • The molecules are in constant motion. This motion is different for the 3 states of matter. • Solid - Molecules are held close to each other. They will vibrate (wiggle and jiggle), but will stay in close proximity. • Solids usually maintain both their shape and their volume. • Liquid - Molecules will flow, slide or glide over one another, but stay toward the bottom of the container. • Liquids maintain their volume, but not their shape. • Gas - Molecules are in continual straight line motion. They are much farther apart and move freely of each other. • Gases do not maintain shape or volume. They will expand to fill a container of any size.

4. Temperature • Temperature is a measure of the average kinetic energy of the molecules of a substance. • The warmer something is the more kinetic energy its atoms possess • Temperature can be measured with a thermometer. • Farenheit – American unit for measuring temperature • Celsius - Metric unit for measuring temperature • Kelvin – Scientific unit for measuring temperature • Absolute Zero – The lowest theoretical temperature. Atoms lose all kinetic energy and are no longer moving. • -273 degrees C, 0 Kelvin

5. Vocabulary to know! • Heat – the thermal energy transferred from one substance to another due to temperature differences between the substances • Specific Heat – The amount of heat needed to raise the temperature of 1 gram of substance1 degree Celsius. • calories (cal) – a unit for measuring heat energy • Joules (J) – another unit for measuring heat energy • **Note: 4.18 J = 1 cal

6. Laws of thermodynamics • Energy can be neither created nor destroyed. It can only change forms. In any process in an isolated system, the total energy remains the same. • Heat always flows from hot substances to cold substances. • No system that we’ve seen can reach absolute zero- no motion at all!

7. For Today’s Lab • Calculating Thermal Energy Transfer • Q= mcDT • Q-thermal energy gained = (m-mass) x (c- specific heat) x (DT- Tfinal - Tinitial - change in temperature) • Specific heat of water - 1 cal/g•°C or 4.18 J/g•°C • Remember: 1 mL of water has a mass of 1 gram • Example: How much energy is required to heat 10g of water from 10 degrees Celsius to 20 degrees Celsius? • 10g • (1 cal/g°C) • (20°C– 10°C) = ?

8. How many calories are required to change the temperature of 22.5g of water from 86degreesC to 52 degrees C? • If it requires 322 calories to heat 86.5g of water and the starting temperature is 12 degrees C, what is the final temperature?

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