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 increasing Entropy= disorder

Third Law of Thermodynamics  The entropy of an ideal solid at zero Kelvin is zero All 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 melting Water evaporating

Exothermic Reactions  Gives off energy during a reaction  Reactants have more energy than products  Gives off heat Ice freezing Water 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: 3Hn09OBs&safety_mode=true&persist _safety_mode=1 3Hn09OBs&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 5  C? (specific heat of Hg is J/g  C)  If 68,000J of heat are added to 25g of H 2 O (specific heat of water is J/g  C), 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  q substance1 = - q substance2 since q = m C ∆ T… m 1 C 1 ∆ T 1 = - m 2 C 2 ∆T 2

 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 J/g°C, calculate the specific heat of the metal.