Energy
Dec 28, 2015
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