Energy

10.1 The Nature of EnergyEnergy: the ability to do

work or produce heat Potential energy (store

energy): energy due to position or composition

Kinetic energy (motion energy): energy due to motion of the object and depends on the mass of the object and its velocity KE = ½ (mv2)

Law of conservation of energy: that energy can be converted from one from to another but can be neither created or destroyed. Energy of the universe is

constant

The nature of energyWork: force acting over

a distanceW = F/d

State function: property of the system that changes independently of its pathwayWhich of the following are

state functions, and which are not

The temperature of an ice cube

The volume of an aerosol can

The amount of time required for a 10 mi bike ride

10.2 Temperature and HeatTemperature: is a measure of the random

motions of the components of a substanceE.g H2O molecules move rapidly in hot water

than in cold waterHeat: a flow of energy due to a temperature

differenceTfinal = average temp from mixing (hot & cold

temp)

10.3 Exothermic and Endothermic Process System –

everything we focus on in experiment

Surroundings – everything other the system

exothermic (energy flows out of system to surrounding (via heat)

endothermic ( energy flows into system from surrounding (via heat)

ExamplesIdentify whether these process are

exothermic or endothermicYour hand gets cold when you touch iceThe ice melts when you touch itPropane is burning in a propane torchTwo chemicals mixing in a beaker give off heat

10.4 ThermodynamicsIs the study of energy.First law of thermodynamics: the energy of

the universe is constantInternal energy – energy of the system

∆E = q x w∆ => change in the functionq => represents heatW => represents work

10.5 Measuring Energy changescalorie: the amount of energy (heat) required

to raise the temperature of one gram of water by 1oC1Calorie = 1000 calories

Joule (J) – SI unit1 calories = 4.184 joules

Converting Calories to JoulesExpress 60.1 cal of energy in units of joules

How many calories of energy corresponds to 28.4 J?

Specific heatThe amount of

energy required to change the temperature of one gram of a substance by 1oCDenoted as s

Heat required = specific heat x mass x change in temp

q = s m ∆T

Calculating Energy RequirementsDetermine the amount of energy (heat) in joules

required to raise the temperature of 7.40 g water from 29.0oC to 46.0oC

A 5.63 g sample of solid gold is heated from 21oC to 32oC. How much energy in Joules and calories is required?

A sample of gold requires 3.1 J of energy to change its temperature from 19oC to 27oC. What is the mass of this sample of gold

A 55.0 g aluminum block initially at 27.5oC absorbs 725 J of heat. What is the final temperature?

10.6 EnthalpyHeat of reaction (∆H) = the amount of heat that being

absorbed or release by a given reaction∆Hp = heat

EnthalpyWhen 1 mol of methane (CH4) is burned at

constant pressure, 890 kJ of energy is released at heat. Calculate ∆H for a process in which a 5.8 g sample of methane is burned at constant pressure

The reaction that occurs in the heat packs used to treat sports injuries is

4Fe(s) + 3 O2(g) 2Fe2O3(s) ∆H= -1652 kJHow much heat is released when 1.00 g of Fe(s) is reacted

with excess O2(g)

EntropyEntropy (S) – measure of

disorder or randomnessRandomness increase -> S

increasesSgas> Sion >Smolecule>Ssolid

Ssolid = 0

E.gH2O(s) H2O (l) S = +

H2O (l) H2O (g) S = +

H2O (g) H2O (l) S = -

2nd law of thermodynamic: the entropy of the universe is always increasing