1. Thermochemistry
Feeling hot, hot, hot

2. heat chemical temp. difference joule
Thermochemistry
Thermochemistry – concerned with the changes that occur during a
reaction.
Heat ( ) that transfers from one object to another because of a
between them.
SI unit is the ( ). Heat always flows from a object to a
object.
heat
chemical
energy q
temp. difference
joule J
warmer
cooler

3. Heat transfer
Example: You place an ice cube into a bowl of hot soup. Describe the direction of heat flow.
The hotter soup transfers heat to the colder ice.
It is possible to transfer HEAT, but never COLD. (There is no such thing as cold transfer!)

4. (Stored within the chemical structure of molecules)
Energy
Energy – the for doing or supplying
capacity
heat
work
Kinetic energy
Potential energy
Due to motion
Due to position
(Temperature)
(Stored within the chemical structure of molecules)

5. release ALL absorption Law of COE created destroyed transferred
Law of Conservation of Energy – Energy is neither nor ; it can from one form to another.
chemical reactions involve a
or of heat.
created
destroyed
transferred
ALL
release
absorption

6. releases heat absorbs heat
Reactions
exo - exit
Exothermic process –
to its surroundings
Endothermic process –
releases heat
absorbs heat
endo - enter

7. Reactions Direction of heat flow Sign Reaction Type
Heat flows OUT of the system
Negative –
“Losing heat”
Exothermic
Heat flows INTO the system
Positive +
“Gaining heat”
Endothermic

8. Thermochemical Equations
4Fe (s) O2 (g)  2Fe2O3 (s) kJ
Does this reaction give off heat or absorb heat?
Exothermic or endothermic?

9. Thermochemical Equations
What does kJ mean?
(measurement of )
ΔH - change in heat content for a reaction at constant pressure.
Kilojoule = 1000 J
heat
Enthalpy

10. Thermochemical Equations
C (s) S (s) kJ  CS2 (l)
Is heat released or absorbed in this chemical reaction?
Exothermic or endothermic?

11. Heat Capacity and Specific Heat
The heat energy required to raise the temperature of 1 g of a substance by 1 degree Celsius.
calorie –the quantity of heat to
needed to raise the temperature
of one g of pure water to one °C.
Q = mcΔT

12. Where Q = the change in heat
m = the mass of water (in grams)
c = the specific heat capacity of water
ΔT = the change in temperature
(Tfinal - Tinitial)

13. Conversions
Convert 444 calories to joules.

14. Measuring/Expressing Heat Changes
Thermochemical equations – treat heat change ( ) just like any other or
Chemistry problems involving H are similar to
problems – depends on number of of reactants and products involved. H
reactant
product
stoichiometry
moles

15. Energy Change in Exothermic and Endothermic Reaction

16. Calculate: Examples
1. Convert the following heat quantities recalling 1 cal= 4.184J
350 cal to joules
515 j to calories
1.6 kcal to joules
2. How much heat is required to change the temperature of 150 g of water by 20 C?
3. How much heat will be given off when 1500 g of water cools down by 20 C?

17. You Do….Pair
What is the total number of joules of heat energy absorbed by 15 g of water when it is heated from 30 C to 40 C?