Chapter 2.1 : Energy

Matter and Energy

Explain that physical and chemical changes in matter involve transfers of energyEnergy : capacity to do work

Move an objectForm a new compoundGenerate light

Always involved in a change of matter.

Physical change : change matter from 1 form to another without changing identity of substance.Water boiling EvaporationWax melting

Chemical Change : change in matter into entirely new substance.Combustion of candle – Changed into CO2 and H2O

Objective 1 :

Matter and Energy

Apply the law of conservation of energy to analyze changes in matterLaw that states that energy cannot be created or

destroyed, just changed from 1 form to another.2 Types of processes

Endothermic : energy is absorbed Example: melting ice, ice pack

Exothermic : energy is released Example: freezing of water, Explosive reactions (TNT)

System : part being studiedIce cube

Surroundings : everything elseair around ice cube

Transfer of energy in different formsPhotosynthesisLight stickCombustion in a car

Objective 2

Exothermic and Endothermic Changes

Distinguish between heat and temperature.Heat : energy transferred between objects

Ice cube melting on a hot day – physical changeCandle burning – chemical change

Energy released as heatGrandcamp explosion

Kinetic energy – energy of motionEnergy absorbed as heat

Baking powder in a cake2NaHCO3 Na2CO3 + H2O + CO2

Heat is needed for reaction to occur

TemperatureMeasure of the average kinetic energy of

the particles in an object

Objective 3

Heat versus Temperature

Convert between the Celsius and Kelvin temperature scalesDifferent Temperature scales

Celsius(oC) Fahrenheit(oF) Kelvin(K)

Objective 4

0

100

212

373

27332

Kelvin Temperature scaleAbsolute zero – all particle movement stops

t(oC) = T(K) – 273.15 T (K) = t (oC) + 273.15

May not affect temperatureHeat of vaporization Heat of fusion

Transfer of heat

Energy added as heat

Tem

pera

ture

O oC

100

oC

Affects substances differentlySpecific heat :

Quantity of heat needed to raise a certain mass of substance 1 oC

Express in (J/g.K)Examples:

Water – high specific heatMetal – low specific heat

Transfer of heat