energy a give and take. 10.1 the nature of energy energy: the ability to do work or produce heat...
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EnergyA Give and Take
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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
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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
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The nature of energyWork: force
acting over a distancew = F x d
State function: property of the system that changes independently of its pathway
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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)
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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)
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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
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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
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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
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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
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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
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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
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Calculating Energy Requirements
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725 J = Tf – 27.5 °C
48.95J/°C 14.8 °C = Tf – 27.5 °C
Tf = 42.3 °C
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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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