1. Chapter 10: Energy Honors Chemistry

4. What is energy? The ability to do work or produce heat

5. But first… State function: a property that changes independently of its pathState function: a property that changes independently of its path Real life examples:Real life examples: DisplacementDisplacement TanningTanning Chemistry examples:Chemistry examples: Changes in energyChanges in energy Changes in temperatureChanges in temperature ∆X = X final – X initial

6. Two general classes of energy: Potential energy: Energy that has the potential of being converted to other forms of energy (like kinetic energy) and do work in the process Think: Water behind a dam Raised object Two charges separated in space Kinetic energy: Energy due to motion

7. Law of Conservation of Energy Energy can neither be created nor destroyed It can only be converted from one form to another

8. Thermodynamics! The study of energy Law of Conservation of Energy is AKA the First Law of Thermodynamics: The energy of the universe is constant!

9. Types of energy… Radiant energy: comes from the sun and is earth’s primary energy source Thermal energy: energy associated with the random motion of atoms and molecules Chemical energy: energy stored in chemical bonds Nuclear energy: energy stored in the neutrons and protons of an atom Electrical energy: potential energy associated with the forces between charged particles Light energy

10. Hot! Hot! Hot! Heat: energy transferred from a hotter object to a colder one Heat flows due to temperature differences No temperature difference = no heat flow Symbolized by q (or Q)

12. More on heat… What was heat again?!? Your answer: Heat cannot be measured directly Changes due to heat can be measured How do you think we do this?!?

13. Temperature… 100°C Hi TE 25°C Med TE 0°C Lo TE Temperature is a measure of the thermal energy of something Thermal energy is how much random movement there is Temperature ≠ thermal energy But the greater the thermal energy, the higher the temperature

14. Defining a system and its surroundings… System: part of the universe being studied Usually reactants and products Surroundings: everything else in the universe Surroundings: Everything else System: Reactants and Products in flask

15. Thermochemistry is the study of heat change in chemical reactions open mass & energyExchange: closed energy isolated nothing SYSTEMSURROUNDINGS System:

16. Exothermic vs. Endothemric Processes Exothermic Process that gives of energy Energy flows out of the system 2H 2 (g) + O 2 (g)  2H 2 O (l) + Energy H 2 O (g)  H 2 O (l) + Energy Endothermic Process that requires energy Energy flows into the system Energy + 2HgO (s)  2Hg (l) + O 2 (g) Energy + H 2 O (s)  H 2 O (l)

17. Exothermic Reaction Reactants have more potential energy than products Potential energy is stored in chemical bonds Amount of energy released by system (c)

18. Endothermic Reaction Reactants have less potential energy than products Amount of energy absorbed by the system (c)

19. ExothermicEndothermic Reactants 2H 2 (g) + O 2 (g)  2H 2 O (l) + Energy Products Energy + 2HgO (s)  2Hg (l) + O 2 (g)

20. ∆E = E final – E initial ∆E = E products – E reactants ∆E = (–) number ExothermicEndothermic Reactants 2H 2 (g) + O 2 (g)  2H 2 O (l) + Energy Products Energy + 2HgO (s)  2Hg (l) + O 2 (g) ∆E = E final – E initial ∆E = E products – E reactants ∆E = (+) number

21. Measuring Energy Changes Calorie: amount of energy (heat) required to raise 1g of H 2 O by 1  C Unit = cal Kilocalorie: 1000 calories Used to measure energy content of food Unit = kcal or Cal

22. More units of energy… Joule (SI unit of energy) Unit = J 1 cal = 4.184 joules

23. Energy required to change temperature depends on… 1.Amount of substance being heated (grams) 2.Temperature change (°C or K) 3.Material that is being heated Different materials respond differently to transfer of heat Know: 1 cal, or 4.184 J, of energy raises the temperature of 1 g of H 2 O by 1°C But… 4.184 J of energy raises the temperature of 1 g of silver metal by 17°C!! Think: wooden vs. metal spoon!

24. Specific Heat Capacity Amount of energy (heat) required to change the temperature of 1g of a substance by 1  C Unit = J/g °C = Jg -1 °C -1 Symbolized by “s” (“c” in other books?!?) See table on page 279…

25. Heat requirements… Q = m x s x  T Q = amount of energy (heat) required to heat up or cool down a sample m = mass of sample (g) s = specific heat capacity of sample  T = change in temperature desired