1 THERMOCHEMISTRY or Thermodynamics

2 Energy & Chemistry ENERGY is the capacity to do work or transfer heat. HEAT is the form of energy that flows between 2 objects because of their difference in temperature. Other forms of energy — lightlight electricalelectrical kinetic and potentialkinetic and potential

3 Energy & Chemistry All of thermodynamics depends on the law of CONSERVATION OF ENERGY. The total energy is unchanged in a chemical reaction.The total energy is unchanged in a chemical reaction. If PE of products is less than reactants, the difference must be released as KE.If PE of products is less than reactants, the difference must be released as KE.

4 Internal Energy (E) PE + KE = Internal energy (E or U) Int. E of a chemical system depends on number of particles type of particles temperature

5 Potential & Kinetic Energy

6 Thermo- dynamics molecular motions the science of heat transfer (molecular motions). Heat transfers until thermal equilibrium is established.

7 Directionality of Heat Transfer Heat always transfer from hotter object to cooler one. Heat lost = heat gained EXO thermic: heat transfers from SYSTEM to SURROUNDINGS. T(system) goes down T(surr) goes up (until it reaches equilibrium

8 Directionality of Heat Transfer Heat always transfer from hotter object to cooler one. Heat lost = heat gained ENDO thermic: heat transfers from SURROUNDINGS to the SYSTEM. T(system) goes up T (surr) goes down

9 ENERGY TRANSFER 1.IDENTIFY SURROUNDINGS AND SYSTEM. 2.EXOTHERMIC OR ENDOTHERMIC ?

10 WORK?

11 Heat is NOT temperature The increased volume with temperature causes the mercury to rise

12 UNITS OF ENERGY 1 calorie = heat required to raise temp. of 1.00 g of H 2 O by 1.0 o C cal = 1 kcal = 1 Calorie (a food “calorie”) = 1 Calorie (a food “calorie”) James Joule But we use the unit called the JOULE 1 cal = joules

13 HEAT TRANSFER The quantity of heat transferred depends on : 1.The quantity of material 2. The size of the temperature change 3. The identity of the material gaining or losing heat

14 HEAT CAPACITY Specific heat = The heat required to raise 1 g of substance 1 ˚K.

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16 Heat Calculations Specific heat capacity (J/ g * K) Heat transfer (J) Mass of substance (g) Change in temperature (K) q = C * m * ∆T

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19 Specific Heat Capacity If 25.0 g of Al cool from 310 o C to 37 o C, how many joules of heat energy are lost by the Al? heat gain/lose = q = (sp. ht.)(mass)(∆T)

20 Specific Heat Capacity where ∆T = T final - T initial q = (0.897 J / gK)(25.0 g)( )K q = J Notice that the negative sign on q signals heat “lost by” or transferred OUT of Al.

21 Change of State: Heat of Fusion Ice J/g (heat of fusion) -----> Liquid water q = (heat of fusion)(mass) constant T

22 Heat water Evaporate water Melt ice Heating/Cooling Curve for Water Note that T is constant as ice melts

23 Heat of fusion of ice = 333 J/g Specific heat of water = 4.2 J/gK Heat of vaporization = 2260 J/g Heat of fusion of ice = 333 J/g Specific heat of water = 4.2 J/gK Heat of vaporization = 2260 J/g What quantity of heat is required to melt 500. g of ice and heat the water to steam at 100 o C? Heat & Changes of State +333 J/g J/g

24 1. melt ice 0 o C q = (500. g)(333 J/g) = 1.67 x 10 5 J 2.water from 0 o C to 100 o C q = (500. g)(4.2 J/gK)( )K = 2.1 x 10 5 J 3.To boil water 100 o C q = (500. g)(2260 J/g) = 1.13 x 10 6 J 4. Total q = 1.51 x 10 6 J = 1510 kJ Heat & Changes of State

25Calorimeter