Energy Notes

• Energy – is the capacity to do work
• Units of energy = Joules (J)
• Energy changes accompany all reactions in Chemistry.
• Heat can be released, or absorbed.
• We will discuss energy in terms of a “system” and it’s interactions with the “surroundings”.
• System = all substances undergoing a change, everything in chemistry is relative to these
• Surroundings = everything else

Types of Energy

• Kinetic energy – energy of motion
• Potential energy – stored energy of an object

1.) Gravitational potential – due to gravity

2.) Chemical potential – energy stored in chemical bonds

• Thermal energy –
• Heat 🡪 always flows from “hot to cold”
• Temperature – measure of average kinetic energy of all the molecules, as temperature increases the molecules speed up, expressed in Kelvin (K)

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Other Types of Energy

• Light energy
• Electric energy
• Hydroelectric energy
• Nuclear energy
• Geothermal energy
• Wind energy

Methods of Heat Transfer

• The science of how heat flows is called heat transfer.
• There are three ways heat transfer works: conduction, convection, and radiation

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Conduction

Transfer of heat between molecules that are physically touching each other; this is a result of objects being at different temperatures.

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Heat always moves from the warmer region to the colder region.

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Example: Ice melting in your hand

Convection

The transfer of energy between an object and its environment, due to fluid motion (through a liquid or gas).

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Caused by the circulation or movement of molecules

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Example: when the bubbles in boiling water rises to the top of the pot

Radiation

Energy is transmitted in the form of waves (electromagnetic radiation) and transformed into kinetic energy.

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Example: the sun warming the earth

Practice

• A hot air balloon rising
• Warming yourself in front of a fireplace
• Cooking food in a microwave oven
• Frying bacon
• Burning your hand on a curling iron
• It is warmer in the attic than in the first floor of your house
• Warm liquid rising, cool liquid sinking
• The sun ray’s
• Burning your feet on hot sand
• Heating a swimming pool

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Heat flow depends on the temperature difference.

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Thermal Equilibrium

• Two bodies are in thermal equilibrium with each other when they have the same temperature.
• In nature, heat always flows from hot to cold until thermal equilibrium is reached.

Internal Energy

• Internal energy – refers to all of the energy contained within a chemical system

(E_total = E_kinetic + E_potential)

• We cannot measure the total internal energy (E) of a system, but we can measure changes (∆E) in internal energy
• Change in internal energy = amount of energy exchanged between a system and its surroundings during a physical or chemical change:
• ∆E = E_final - E_Initial

Law of conservation of Energy

Energy can’t be created or destroyed.

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• Therefore the same amount of energy leaving a system will enter the surroundings!!!