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THERMODYNAMICS
Energy and energy transformations
First Law of Thermodynamics Energy is never created nor destroyed
Energy can change forms, but the quantity is always constant.
Second Law of Thermodynamics
The Entropy of the Universe is always increasingEntropy= disorder
Third Law of Thermodynamics
The entropy of an ideal solid at zero Kelvin is zeroAll molecular motion stops at 0 K
Endothermic Reactions Energy is used to
begin a reaction Products have
higher energy than reactants
Absorbs heat from surroundings Ice meltingWater evaporating
Exothermic Reactions Gives off energy
during a reaction Reactants have
more energy than products
Gives off heat Ice freezingWater condensing
Heat vs Temperature
Temperature - measure of average KE
Heat - measure of energy transfer
Temp change (∆T) depends on: amount of heat
transferred (q) mass of object (m) specific heat of the object
(C) Video link: http://
www.youtube.com/watch?v=wTi3Hn09OBs&safety_mode=true&persist_safety_mode=1
Measuring Heat q = m C ∆T
q = heat○ measured in joules (J)
or kilojoules (kJ) ○ 1000J = 1kJ
m = mass; measured in grams (g)
∆ T = change in temp○ measured in Celsius
(°C) or Kelvin (K)C = specific heat
○ units are J/g°C or J/gK
Endo/exothermic -q = release heat (exothermic) +q= absorb heat (endothermic)
What amount of heat is needed to increase the temp of 10 g of Hg by 5C? (specific heat of Hg is 0.139 J/gC)
If 68,000J of heat are added to 25g of H2O (specific heat of water is 4.184 J/gC), what is the change in temperature in Celsius?
Calorimetry Calorimetry
uses a closed system (calorimeter) to determine the energy change or specific heat of an unknown substance
Calorimeter- an insulated device usually filled with water or a substance with a known specific heat
1st law - conservation of energy When applied to a closed system, any
energy that is lost by one substance is gained by the other
qsubstance1 = - qsubstance2
since q = m C ∆ T…
m1 C1 ∆ T1 = - m2 C2 ∆T2
Ex: A 55.8g piece of unknown metal at 180°C is placed into 100.0g of water that began at 25°C. The final temperature of both was 26.8°C. If the specific heat of water is 4.184 J/g°C, calculate the specific heat of the metal.