1. Enthalpy EQ: How do you predict the sign of delta H?

2. A. Enthalpy (ΔH) 1.Enthalpy is the amount of heat in a system 2.In order to determine the amount of heat change in a reaction we use… 3.Reactions can be… ΔH rxn = H products - H reactants

3. A. Enthalpy (ΔH) A) Endothermic 1.Products have more energy than the reactants 2.ΔH=+ (positive) 3.heat into system 4.Heat is being absorbed 5.Surroundings feel cool 6.Ex: 25 kJ + NH 4 NO 3  NH 4 + + NO 3 - Heat is going into the arrow (energy on the left)

4. A. Enthalpy (ΔH) A) Exothermic 1.Reactants have more energy than products 2.ΔH= - (negative) 3.heat exits system 4.Heat is being released 5.Surroundings feel warm 6.Ex: 4Fe + 3O 2  2 Fe 2 O 3 + 1625 kJ Heat exits the arrow (energy on the right)

5. HEATHEATHEATHEATHEATHEATHEATHEAT

6. Endo or Exo?

7. Endo or Exo

8. Endo or Exo?

10. B. Enthalpy of Combustion (ΔH comb ) 1. change in enthalpy when 1 mol of a substance is completely burned

11. B. Enthalpy of Combustion (ΔH comb ) Ex: How much heat is evolved when 54.0 g C 6 H 12 O 6 is burned? C 6 H 12 O 6 + 6O 2  6 CO 2 + 6H 2 O (ΔH comb = -2808 kJ) 54.0 g C 6 H 12 O 6 180.14 g C 6 H 12 O 6 1 mol C 6 H 12 O 6 -2808 kJ 1 mol C 6 H 12 O 6 = -842 kJ Use coefficient in balanced equation x x

12. C. Molar Enthalpy (heat released per mole) 1.Molar Enthalpy of vaporization: Heat required to evaporate one mole of a substance. 2.Molar Enthalpy of condensation -ΔH Cond = + ΔH VAP

13. 3.Molar Enthalpy of fusion: Heat required to melt one mole of a substance 4.Molar enthalpy of freezing (ΔH solid ) solidification -ΔH Solid = + ΔH Fusion C. Molar Enthalpy (heat released per mole)

14. 5.If the ΔH fus is 6.01 kJ/mol, than the ΔH solid = -6.01 kJ/mol C. Molar Enthalpy (heat released per mole)

15. 6.Ex: Calculate the energy required to melt 250 g of ice. (ΔH fus = 6.01 kJ/mol) 250 g H 2 O 18.02 g H 2 O 1 mol H 2 O 6.01 kJ 1 mol H 2 O =83 kJ C. Molar Enthalpy (heat released per mole) xx

16. Calculate how much energy is absorbed when 7.20 moles of O 2 reacted with an unlimited amount of chlorine. 2Cl 2 + 7O 2 + 130 kcal 2Cl 2 O 7 7.20 moles of O 2 7 moles O 2 +130 kcal = 134 kcal D. More Enthalpy Stoichiometry ΔH = +130 kcal (+ because it’s endo) x

17. Determine the mass of iron used to produce 250 kJ of heat according to the balanced reaction below. 4Fe + 3O 2  2Fe 2 O 3 + 1625 kJ -250 kJ D. More Enthalpy Stoichiometry ΔH = -1625 kJ (- because it’s exo) x -1625 kJ 4 mol Fe x 1 mol Fe 55.85 g Fe = 34 g Fe Produce = - energy