1. HEAT

2. TEMPERATURE AND HEAT Temperature Heat
Measure of the average kinetic energy of the particles in a substance
Heat
The transfer of energy from one substance to another due to temperature differences
Always from high E to low E

3. THE NATURE OF ENERGY Energy The ability to do work or produce heat
2 types: potential and kinetic

4. Potential Energy
Potential energy - is the energy stored in a body or in a system

5. Kinetic Energy
Kinetic energy - energy which it possesses due to its motion
Depends on the mass of the object and its velocity

6. More Kinetic energy

7. More about Energy Law of Conservation of Energy
Energy can be converted from one form to another but cannot be created or destroyed

8. So lets talk about heat…

9. We can measure heat… q = m x ∆T x c q = heat m = mass
∆T = change in temperature
Tfinal – Tinitial
c = specific heat capacity (specific heat)
The quantity of heat required to raise temperature of an object 1oC

10. Using the formula We need 3 out of the 4 so we can solve for the 4th
q = m x ∆T x c
If have q, m, and c – what solving for?
If have m, c, and ∆T – what solving for?

11. Value of “q” What is “q” – HEAT q can be positive or negative
If q is positive – energy is added
The reaction is endothermic
If q is negative – energy is removed/leaving
The reaction is exothermic

12. You said what??
Exothermic process: a change (ie. a chemical reaction) that releases heat.
Ie: Burning fossil fuels
Think “exit”
Endothermic process: a change (ie. a chemical reaction) that absorbs heat.
Photosynthesis is an endothermic reaction (requires energy input from sun)
Think “into”

13. Sample Problem
PCl3 is a compound used to manufacture pesticides. A reaction requires that g of PCl3 be raised from 31.7 oC to 69.2 oC. How much energy will this require given that the specific heat of PCl3 is J/g oC?
A quantity of water is heated from 25.0 oC to 36.4 oC by absorbing 325 J of heat energy. What is the mass of the water? The specific heat of water is J/g oC.

14. Heat Transfer

15. Heat Transfer Heat will transfer from one object to something else
This is a transfer of energy from a place of high E to a place of low E
The transfer of E will change the temperatures

16. Heat Transfer in Water… But what about temperature?
Exothermic reaction: heat given off
-temperature of water will increase
-temperature of object will decrease
UNTIL temperature of water and object are equal!!
Therefore Tfinal for water and object are the same
reaction

17. (con.) Endothermic reaction: heat taken in
-temperature of water will decrease
-temperature of object will increase
UNTIL temperature of water and object are equal!!
Therefore Tfinal for water and object are the same
reaction

18. Therefore… - q lost = q gained We can say that: q lost = q gained
But wait… one is going to be negative
Therefore we must:
- q lost = q gained

19. But what does q equal? -(m x ∆T x c) = m x ∆T x c - q lost = q gained
q = m x ∆T x c
Therefore we can say that:
- q lost = q gained
-(m x ∆T x c) = m x ∆T x c

20. Enthalpy of Fusion

21. Enthalpy of fusion: Hfus
The energy needed to melt a solid into a liquid
As energy is added to a solid at its melting point, all the energy is used to increase the kinetic energy of the molecules during the phase change.
Because of this, the temperature of the melting system remains constant until all of the solid has become liquid. If energy is still being added to the system, the temperature will begin to climb when all of the solid becomes liquid.

22. Another way to look at it…
When a solid melts, its particles are freed to move with respect to one another.

23. Formula (solid  liquid)
Formula: q = m Hfus
q = heat gained (+) or lost (-)
m = mass
DHfus = heat of fusion
Formula for Heat Transfer with Enthalpy of Fusion
m  Hfus = m  Tc

24. Enthalpy of Solution

25. Enthalpy of Solution
The energy change when one mole of a substance dissolves in water.
Formula: q = m  Hsol
q = heat gained (+) or lost (-)
m = mass
 Hsol = heat of solution
Formula for Heat Transfer with Enthalpy of Solution
m  Hsol = m  Tc