1. Chapter 5.1-5.3 Thermochemistry

2. Thermo means heat or energy Energy: Capacity of doing work Work: Force x displacement

3. Types of Energy Kinetic Energy (KE) Energy due to motion E k = ½ mv 2 Where m = mass & v = velocity

4. Types of Energy Potential energy (PE) Energy due to position Gravity higher PE lower PE Units: Calorie (cal), Joule (J) 1 Cal = 4.184 J

5. System Where we focus our attention Surroundings Everything else

6. First Law of Thermodynamics Energy is conserved Piston pushed up & work (W) done by the gas (say 6 J) 10 J added (q)

7. First Law of Thermodynamics What happens to the difference (10 – 6)? Retained inside. (causes Internal energy change, ΔE): 10 = 4 + 6 q (Heat applied) = ? q = ΔE + W (first law Thermodynamics) or ΔE = q-W (here -W, Work done by the gas) ΔE = q +W (here +W, Work done on the gas) Note: Two different sign conventions exist

8. Enthalpy (H) q = ΔE + P ΔV ΔE = q-W (work done by a gas) ΔH = ΔE + P ΔV (constant pressure) H = E + PV q = ΔE + W

9. Enthalpy or heat Content (H) Begin End 2H 2 + O 2  2H 2 O Say 484 kJ 1 kJ Note: 484 kJ is the Heat content of the reactants (H R ) and 1 kJ is the heat content of the products (H P ).

10. Enthalpy or heat Content (H) ΔH =H p –H R =1 – 484 =-483 kJ (exothermic) Here, initial heat content> Final heat cont. What happens to the difference? It is given off.

11. Enthalpy or heat Content (H) 2H 2 O  2H 2 + O 2 1 kJ (H R ) 484 kJ (H P ) Is heat absorbed or given off? Heat is absorbed ΔH =H p –H R =484 – 1 =483 kJ (endothermic) Here, initial heat cont < Final heat cont