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EnergyA Give and Take
10.1 The Nature of Energy Energy: 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 velocityKE = 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 x d
State function: property of the system that changes independently of its pathway
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 water
Heat: a flow of energy due to a temperature differenceTfinal = average temp from mixing (hot
& cold temp)
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
ThermodynamicsIs the study of energy.
First law of thermodynamics: the energy of the universe is constant
Internal energy – energy of the system ∆E = q + w∆ => change in the functionq => represents heatw => represents work
10.5 Measuring Energy changes
calorie: 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?
60.1 cal 4.184 J = 251 J
1 cal
28.4 J 1 cal = 6.79 cal
4.184 J
Calculating Internal Energy
Calculate ΔE for q = 34 J, w = -22 J
ΔE = q + w
ΔE = 34 J + (-22 J) = 12 J
Is this exothermic or endothermic?ΔE > 0, therefore it is endothermic
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 x m x ∆T
Calculating Energy Requirements
725 J = Tf – 27.5 °C
48.95J/°C 14.8 °C = Tf – 27.5 °C
Tf = 42.3 °C
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?
Q = s x m x ΔT
sgold = 0.13 J/g oC
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