1. Mr. Kinton Honors Chemistry
Thermochemistry
Mr. Kinton
Honors Chemistry

2. Thermochemistry
Study of chemical reactions and energy changes involving heat
Major concepts include:
Energy
Work
Heat

3. Energy
Kinetic
Potential
Electrostatic
Chemical
Thermal

4. Energy Kinetic Potential Energy of motion Ek=(1/2)mv2 A moving car
Energy based on position relative to other objects
Gravity is a great example
Ep=mgh

5. Units of Energy SI unit is the joule
We will often use the kilojoule in chemical reactions
Calorie: amount of energy required to raise the temperature of 1g of water from 14.5 to 15.5 degrees celsius
1 cal=4.184 J (exactly)
Nutritional Calorie: 1 Cal=1000 cal= 1kcal

6. How energy moves System Surroundings
The portion we single out for study
Closed system: readily studied
Can exchange heat but not matter
Everything else outside of the system
Allows for the transfer of heat, matter, and energy
Possible due to work and heat

7. Transfer of Energy Motion of an object against a force
Force: push or pull exerted on an object
Work: energy used to cause an object to move against a force
W= F x d
Anything that causes a temperature change
Heat: energy transferred from a hotter object to a colder one
Energy: the capacity to do work or to transfer heat

8. First Law of Thermodynamics
Energy can neither be created or destroyed
Energy is conserved
Energy that is lost by the system is gained by the surroundings

9. Types of Heat Transfer Endothermic Exothermic
Occurs when the system absorbs heat
Heat flows from the surroundings to the system
Feels cold to us
Occurs when the system gives off heat
Heat flows out of the system to the surroundings
Feels warm to us

10. Enthalpy
Thermodynamic function that accounts for heat flow in chemical changes
When delta H is positive= endothermic
When delta H is negative= exothermic
It’s an extensive property (dependent on amounts)
Enthalpy changes are equal in magnitude but opposite in sign for reverse reactions
Enthalpy depends on state of matter

11. Calorimetry Experimentally we can determine enthalpy
Measurement of heat flow (calorimeter)
Heat Capacity: the temperature change experienced by an object when it absorbs energy
Specific Heat: Heat capacity of 1g of a substance
q/ m x delta T
Quantity of Heat: specific heat x g of substance x delta T

12. Example
How much heat is needed to warm 250g of water from 22 degrees Celsius to near its boiling point, 98 degrees Celsius?

13. Constant-Pressure Calorimetry
qrxn= qsoln=-qrxn
This is a general guideline and we will be using it for other calorimetry problems

14. Bomb Calorimetry Calorimetry studies chemical potential energy
Studies combustion reactions under constant volume conditions