1. NOTE: To change the image on this slide, select the picture and delete it. Then click the Pictures icon in the placeholder to insert your own image. 4.3 HEATS OF FORMATION Mrs. Wilson

2. Objectives  Determine the specific heat capacity of an unknown metal by experiment.  Understand and rearrange the different types of reactions commonly found in thermochemistry.  Calculate enthalpy of reaction (ΔH° rxn, ΔH° c ) using heats of formation.  Calculate enthalpy of reaction for a given mass or moles of reactant or product. Homework: Lesson 4.3a homework #1-5 only; Daily Quiz next class.

3. Engage/Explore: What Is That Metal? Objective: Determine the specific heat capacity of an unknown metal by experiment. Materials: 2-3 metal cubes; hot plate; thermometer; tap water; beaker; graduated cylinder. Procedure:  Examine your materials and come up with a plan. Talk to me before you start.  Perform your experiment.  Calculate the specific heat capacity of your metal on the index card I give you. Show all your work, use sig fig rules correctly and the appropriate unit after your final answer. Possible Identities Brass 0.380 Copper 0.385 Iron 0.450 Aluminum 0.902

4. Enthalpy and Thermochemical Equations  the quantity of heat transferred during a change  symbol ΔH; unit kJ/mole  “°” means “standard conditions” of 25°C and 1 atm pressure  A thermochemical equation gives the balanced equation and its associated enthalpy: 2 H 2 O (l)  2 H 2(g) + O 2 (g) ΔH° rxn = - 285.8 kJ/mol H 2 O (s) --> H 2 O (l) ΔH ° = + 6.00 kJ/mol

5. Types of Enthalpy (pg. 6 of packet) ΔH rxn ΔHc ΔHc ΔHf ΔHf ΔH neut (there are other kinds too) Enthalpy of combustion Products are CO 2 and H 2 O Enthalpy of formation Enthalpy of neutralization The energy needed to form 1 mole of compound from “standard states” (most common state of matter) ex) C (s) + ½ O 2(g)  CO (g) (fractions as coefficients are OK here)

6. Calculations involving Thermochemical Equations A. Write the equation if a change has been made

7. (- 714 kJ; 857 kJ)

8. Calculations involving Thermochemical Equations

9. Thermodynamic Reference Table For today’s lesson you’ll only be needing two sections of this reference table.

10. Calculations involving Thermochemical Equations C. Solve for ΔH° rxn or ΔH f ° C 2 H 6 is ethane - 1008.8 kJ/mol - 3121.2 kJ 130.6 kJ

12. Exit Ticket (On the index card.)  Write a balanced thermochemical equation for the combustion of one mole of liquid benzene, C 6 H 6. (ΔH c = - 3267.6 kJ) 2. What is ΔH rxn for the reverse equation from #1?  Calculate the ΔH c for the burning of 100.0 g of benzene.  Calculate the ΔH° f of benzene. (ΔH° f of CO 2 (g) = - 393.5 kJ/mol; H 2 O (g) = - 241.8 kJ/mol)