Friday, Sept. 20th: “A” DayMonday, Sept. 23rd: “B” Day

AgendaCh 1 TestsStart Ch. 2: Matter and Energy

Section 2.1: “Energy”Energy, physical/chemical changes, evaporation,

exothermic/endothermic, law of conservation of energyHomework:

Pg. 45: #1-13Phase Change Diagram WSConcept Review: “Energy”

**Quiz over section 2.1 next time!**

Ch 1 Tests“The Science of Chemistry”

Class Average Score(out of 60)

Percentage

2A4A1B3B

Ch 2: Matter and EnergySec. 2.1: “Energy”

Energy: the capacity to do work, such as moving an object, forming a new compound, or generating light.

Energy is always involved when there is a change in matter.

Changes in Matter can be Physical or Chemical

Physical change: a change of matter from one form to another without a change in chemical properties.

The chemical nature of the substance does not change.

Examples:Ice meltingWater boiling

Changes in Matter can be Physical or Chemical

Chemical change: a change that occurs when one or more substances change into entirely new substances with different properties.

A chemical change occurs whenever a new substance is made.

Example:Reaction of hydrogen + oxygen to produce water

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Every Change in Matter Involves a Change in Energy

All physical AND chemical changes involve a change in energy.

Sometimes, energy must be supplied for the change in matter to occur.

Example: for ice to melt, energy must be supplied so

that the particles have enough energy to slide past one another

Every Change in Matter Involves a Change in Energy

If more energy is added to the melted ice and the boiling point is reached, the particles of the liquid will leave the liquid’s surface through evaporation.

Evaporation: the change of a substance from a liquid to a gas.

Energy and ChangeSometimes, energy is released when a change

in matter occurs.Examples:

Energy is released when a vapor turns into a liquid (condensation)

Energy is released when a liquid turns into a solid (freezing)

Energy is released when hydrogen and oxygen combine to form water

Endothermic/Exothermic Processes

Endothermic: describes a process in which heat is absorbed from the environment

ExamplesIce meltingWater boiling

Endothermic/Exothermic Processes

Exothermic: describes a process in which a system releases heat into the environment

ExamplesWater freezingWater condensing into

liquid from vaporHydrogen + oxygen form

water

Conservation of Energy

Law of conservation of energy: the law that states that energy cannot be created or destroyed but can be changed from one form to another.

During any chemical or physical change, the total quantity of energy remains constant.

Energy is Often Transferred

To keep track of energy changes, chemists use the terms system and surroundings.

System: all of the components that are being studied at any given time

Surroundings: everything outside of the system

Conservation of Energy in a Chemical Reaction

An exothermic process involves a transfer of energy from a system to its surroundings.

An endothermic process involves a transfer of energy from the surroundings to the system.

The total energy of the systems and their surroundings remains the same.

Conservation of Energy in a Chemical Reaction

Does this chart represent an exothermic or endothermic process?

Energy Can be Transferred in Different Forms

The transfer of energy between a system and its surroundings can involve different forms of energy:Chemical MechanicalLightHeatElectricalSound

Heat

Heat: the energy transferred between objects that are at different temperatures; energy is always transferred from higher-temperature objects to lower-temperature objects until thermal equilibrium is reached.

Kinetic energy: the energy of anobject that is due to the object’smotion

Energy Can be Released or Absorbed as Heat

Exothermic reactionEnergy is released as heat

Endothermic reactionEnergy is absorbed as heat

Heat is Different From Temperature

Temperature: a measure of how hot or cold something is; specifically, a measurement of the average kinetic energy of the particles in an object.

Temperature is Expressed Using Different Scales

The two temperature scales that are used in chemistry are:Celsius, ˚CKelvin, K

0˚C = freezing point of water0 K = absolute zero, the temperature at which

the minimum average kinetic energies of all particles occur

To find °C = T(K) - 273 To find K = t(˚C) + 273

Transfer of Heat May Not Affect Temperature

Heating Curve for Water

Transfer of Heat May Not Affect Temperature

Notice that the temperature only increases when the substance is in the solid, liquid, or vapor states.

The temperature does not increase when the solid is changing to a liquid or when the liquid is changing to a gas.

The energy that is added is used to change state.

Specific Heat

Specific Heat: the quantity of energy, as heat, that must be transferred to raise the temperature of 1 g of a substance 1 K or 1˚C.

The SI unit for energy is the joule (J)Specific heat is expressed in:

joules per gram kelvin (J/g · K)

Specific HeatMetals tend to have low specific heats, which

indicates that relatively little energy must be transferred as heat to raise their temperatures.

Water has an extremely high specific heat.

This is why a metal pot gets hot fast but the water inside it takes a long time to warm up.

Specific Heat

This is also why Lake Michigan is always so cold, even in August!

It takes a long time to warm something, like water, that has a high specific heat.

HomeworkSection 2.1 review, pg. 45: #1-13Phase Change Diagram worksheetHomework: Concept Review: “Energy”

**Next time: Sec 2.1 Quiz**