1. Thermochemistry

2. Thermal Energy
All matter is made of small particles in constant motion
The speed of particle motion increases with the addition of thermal energy
Thermal Energy – the sum of the kinetic and potential energy of all of the atoms in an object

3. Thermal energy increases as temperature increases (q)
Temperature – is the measure of the average kinetic energy of an object’s atoms or molecules
Absolute Zero (-273oC) All molecular motion stops

4. Temperature
Units of temperature include Fahrenheit(F), Centigrade or Celsius (C), and Kelvin (K)
F = (1.8) C0 + 32
K = C

5. Thermal energy only flows from hot to cold.
Heat
Thermal energy that flows from something at a higher temperature to something at a lower temperature is called heat
Thermal energy only flows from hot to cold.

6. 1 calorie (cal) The ability to heat 1 g of water 1oC
Measuring Heat
1 calorie (cal) The ability to heat 1 g of water 1oC
1 Calorie = 1,000 calories also called a kilocalorie or kcal
1000 cal = 4180J or
1 cal = 4.18 J

7. Specific Heat
Specific heat is the amount of energy needed to raise the temperature of a material by 1o C or K
Designated by Cp

8. Units for Measuring Heat
The Joule is the SI system unit for measuring heat:
The calorie is the heat required to raise the temperature of 1 gram of water by 1 Celsius degree

9. Heat (Enthalpy) Change, ΔH
Energy
Energy is the capacity to do work, and can take many forms
Potential energy is stored energy or the energy of position
Kinetic energy is the energy of motion
Thermal energy (heat) is an outward manifestation of movement at the atomic level
Heat (Enthalpy) Change, ΔH
Definition: The amount of heat energy released or absorbed during a process.

10. Calorimetry
The amount of heat absorbed or released during a physical or chemical change can be measured, usually by the change in temperature of a known quantity of water in a calorimeter.

11. Exothermic Processes
Processes in which energy is released as it proceeds, and surroundings become warmer
Reactants  Products + energy

12. Endothermic Processes
Processes in which energy is absorbed as it proceeds, and surroundings become colder
Reactants + energy  Products

13. 4.184 Joules per grams degree Centigrade (J/g 0 C)
SPECIFIC HEAT OF WATER
4.184 Joules per grams degree Centigrade (J/g 0 C)

14. Cp = Specific Heat Capacity at Constant Pressure
Q=(m)(Cp)∆T
Q = Specific Heat
m = mass
Cp = Specific Heat Capacity at Constant Pressure
∆T = Change in Temperature

15. Changes in enthalpy = H
Calorimetry
Changes in enthalpy = H
q = H These terms will be used interchangeably in this textbook
Thus, q = H = m x C x T
H is negative for an exothermic reaction
H is positive for an endothermic reaction

16. Changes in Thermal Energy
When heat flows into an object and it’s temp rises the change is positive
When heat flows out, its temp decreases and the change is negative

17. Chemistry Happens in
MOLES
An equation that includes energy is called a thermochemical equation
CH4 + 2O2 ® CO2 + 2H2O kJ
1 mole of CH4 releases kJ of energy.
When you make kJ you also make 2 moles of water

18. Thermochemical Equations
A heat of reaction is the heat change for the equation, exactly as written
The physical state of reactants and products must also be given.
Standard conditions for the reaction is kPa (1 atm.) and 25 oC

19. CH4 + 2 O2 ® CO2 + 2 H2O kJ
If grams of CH4 are burned completely, how much heat will be produced?
1 mol CH4
802.2 kJ
10. 3 g CH4
16.05 g CH4
1 mol CH4
= 514 kJ

20. How many grams of water would be produced with 506 kJ of heat?
CH4 + 2 O2 ® CO2 + 2 H2O kJ
How many liters of O2 at STP would be required to produce 23 kJ of heat?
How many grams of water would be produced with 506 kJ of heat?

21. Heat of Combustion
The heat from the reaction that completely burns 1 mole of a substance
Heat of Fusion
Molar Heat of Fusion (Hfus) - the heat absorbed by one mole of a substance in melting from a solid to a liquid

22. when a substance vaporizes, energy is needed.
Heat of Vaporization
the heat required to change one mole of a substance from a liquid to a gas
when a substance vaporizes, energy is needed.
when a substance condenses, energy is released.