Presentation is loading. Please wait.

Presentation is loading. Please wait.

Thermochemistry Spring Semester Final Exam Review.

Similar presentations


Presentation on theme: "Thermochemistry Spring Semester Final Exam Review."— Presentation transcript:

1 Thermochemistry Spring Semester Final Exam Review

2 THERMOCHEMISTRY The study of heat released or required by chemical reactions Fuel is burnt to produce energy - combustion (e.g. when fossil fuels are burnt) CH 4 (g) + 2O 2 (g) CO 2 (g) + 2H 2 O(l) + energy

3 What is Energy? Energy Kinetic energy (KE) Potential energy (PE) Energy due to motion Stored energy

4 Total Energy = Kinetic Energy + Potential Energy E = KE + PE Temperature measures the average Kinetic energy & potential energy are interchangeable Heat is the total energy of a system: Kinetic energy + potential energy

5 Systems & Surroundings In thermodynamics, the world is divided into a system and its surroundings A system is the part of the world we want to study (e.g. a reaction mixture in a flask) The surroundings consist of everything else outside the system

6 EXOTHERMIC & ENDOTHERMIC REACTIONS Exothermic process: a change (e.g. a chemical reaction) that releases heat to the surroundings. A release of heat corresponds to a decrease in enthalpy Exothermic process:  H < 0 (at constant pressure) Burning fossil fuels is an exothermic reaction

7 Exothermic Reactions

8 Endothermic process: a change (e.g. a chemical reaction) that requires (or absorbs) heat from the surroundings. An input of heat corresponds to an increase in enthalpy Endothermic process:  H > 0 (at constant pressure) Photosynthesis is an endothermic reaction (requires energy input from sun)

9 Endothermic Reactions

10 exothermic endothermic exothermic endothermic

11 A plot of temperature vs. time that represents the process in which energy is added at a constant rate Courtesy Christy Johannesson Heating Curves Animation

12 Temperature ( o C) Time Melting - PE  Solid - KE  Liquid - KE  Boiling - PE  Gas - KE 

13 A plot of temperature vs. time that represents the process in which energy is added at a constant rate

14 The standard enthalpy of reaction (  H 0 ) is the enthalpy of a reaction carried out at 1 atm. rxn aA + bB cC + dD H0H0 rxn d  H 0 (D) f c  H 0 (C) f = [+] - b  H 0 (B) f a  H 0 (A) f [+] H0H0 rxn n  H 0 (products) f =  m  H 0 (reactants) f  - 6.6

15 Calculate the heat of combustion of methane, CH 4 CH 4 (g) + 2 O 2 (g) CO 2 (g) + 2 H 2 O(g )  H◦ f CH 4 (g) = kJ/mol  H◦ f O 2 (g) = 0 kJ/mol  H◦ f CO 2 (g) = kJ/mol  H◦ f H 2 O(g) = kJ/mo l 15 pg mol( kJ/mol) = kJ Step #1: multiply the  H◦ f H 2 O(g) by 2 since there are two moles of water in the products.

16 Calculate the heat of combustion of methane, CH 4 CH 4 (g) + 2 O 2 (g) CO 2 (g) + 2 H 2 O(g )  H◦ f CH 4 (g) = kJ  H◦ f O 2 (g) = 0 kJ/  H◦ f CO 2 (g) = kJ  H◦ f H 2 O(g) = kJ 16 pg. 316 Step #2: sum up all the  H ◦ f. :  H◦ f = [ kJ + ( kJ)]- [ kJ + (0 kJ )]  H◦ f = kJ  H rxn =   H f (products) -   H f (reactants)

17 Calculations Involving Specific Heat C = Specific Heat Capacity q = Heat lost or gained  T = Temperature change T f - T i OR

18

19

20

21

22 Choose all that apply... C(s) + 2 S(g) CS 2 (l)  H = 89.3 kJ Which of the following are true? A)This reaction is exothermic B) It could also be written C(s) + 2 S(g) kJ CS 2 (l) C) The products have higher energy than the reactants D) It would make the water in the calorimeter colder


Download ppt "Thermochemistry Spring Semester Final Exam Review."

Similar presentations


Ads by Google