1. Thermochemistry
Chemistry One B

2. Energy and Heat
Heat energy can either be needed to start a chemical reaction or it can be given off during a chemical reaction.
Thermochemistry is the study of energy changes that occur during chemical reactions.
Energy- the capacity for doing work or producing heat
Temperature- Measurement of the average kinetic energy of the particles within a substance.

3. Energy and Heat
Heat (q)-energy that transfers from one object to another because of temperature differences between them.
Heat always flows from a warmer object to a cooler object.
EX: Ice in hand

4. Potential and Chemical Energy
Potential Energy- energy that can do work that is stored in chemical bonds
Chemical Energy is available to do work when bonds are broken
Work – The product of energy usage to make something happen

5. Endothermic and Exothermic Reactions
Essentially all chemical reactions and change of state reaction involve either
Absorption of heat (Endothermic)
Release of heat (Exothermic)

6. Endothermic and Exothermic Reactions
In studying heat changes, think of defining these two parts:
The system- the part of the universe on which you focus your attention
The surroundings- includes everything else in the universe
Universe= system + surroundings
A major goal of thermochemistry is to examine the flow of heat between the system and its surroundings.

7. Endothermic and Exothermic Reactions
The Law of Conservation of Energy states that in any chemical or physical process, energy is neither created or destroyed.
If the energy of the system decreases, the energy of the surroundings must increase by the same amount so that the total energy of the universe remains unchanged.

8. Endothermic Reaction
Read and underline key ideas in the paragraph below.
Sometimes a reaction or process requires heat to proceed and the systems will take heat from the surroundings. Since heat is being removed from the surroundings, the reaction vessel will feel cool. This means that the entalpy of the products is higher than the enthalpy of the reactants and heat is one of the reactants. This is called an endothermic reaction (endo=into). A common example of an endothermic process is the melting of ice. Solid water (ice) needs heat energy to help break apart the forces holding it together as a solid. The heat flowing into the ice will cool the surroundings.

9. Endothermic and Exothermic Reactions
Heat flowing into a system from its surroundings:
Defined as endothermic
q (Δ H) has a positive value
System gains heat as the surroundings cool down

10. Exothermic Reactions
Read and underline key ideas in the paragraph below.
When a system releases heat to the surrounding environment during a reaction the temperature of the surroundings increases and the reaction vessel, which is part of the surroundings will feel warm. For this type of reaction, the enthalpy of the products is lower than the enthalpy of the reactants and heat is one of the products. This is called an exothermic reaction (Exo=out of).

11. Endothermic and Exothermic Reactions
Heat flowing out of a system into its surroundings:
Defined as exothermic
q (Δ H) has a negative value
System loses heat as the surroundings heat up

12. Endothermic and Exothermic Reactions
Every reaction has an energy change associated with it
Exothermic reactions release energy, usually in the form of heat
Endothermic reactions absorb energy, usually in the form of heat

13. Endothermic and Exothermic Reactions
ΔH = Heat of Reaction (also known as Enthalpy)
ΔH is measure in KJ or Kilo Joules
Endothermic Rxns:
Heat enters the reaction as a reactant
ΔH (heat of reaction) is positive
Exothermic Rxns:
Heat exits the reaction as a product
ΔH (heat if reaction) is negative
At constant pressure heat (q)= ΔH

14. Endothermic and Exothermic Reactions
NaCl + F KJ  NaF + Cl2
1. Is heat a reactant or product?
2. Is this endothermic or exothermic?
3. Would ΔH be + or -?
4.Re-write the equation:

15. Endothermic and Exothermic Reactions
CH4 + O2  CO2 + H2O KJ
1. Is heat a reactant or product?
2. Is this endothermic or exothermic?
3. Would ΔH be + or -?
4.Re-write the equation:

16. Heat Capacity and Specific Heat
A calorie is defined as the quantity of energy needed to raise the temperature of 1g of pure water 1 degree Celcius.
Calorie is written with a lower case c except when referring to the energy contained in food.
The dietary calorie is written with a capital C, refers to energy in food.
1 C= 1000 c

17. Heat Capacity and Specific Heat
The calorie is also related to the Joule, the SI unit of heat and energy.
4.184 J = 1 cal
Specific Heat Capacity (C) – the amount of the heat it takes to raise the temperature of 1g of the substance 1 degree Celcius
Specific heat for short

18. Heat Capacity and Specific Heat
Water has a high specific heat value compared to other chemicals
For water, C= 4.18J/g ° C
C= 1.00 cal/g ° C
Thus for water:
It takes a lot of heat to raise the temperature
It take a long time to cool off

19. Heat Capacity and Specific Heat
To calculate specific heat, use the formula:
C = q
m x Δ T
Heat is abbreviated a q
Δ T= change in temperature (Tf – Ti)
C= Specific Heat of the substance
Units are either in J/(g deg C) or cal/(g deg C)
m= mass

20. Calorimetry
Calorimetry- the accurate and precise measurement of heat flow into or out of a system for chemical and physical processes.
The device used to measure the absorption or release of heat in chemical or physical processes is called a calorimeter.

21. Calorimetry
Foam cups are excellent heat insulators and are commonly used as simple calorimeters.

22. Summary Thermochemistry is the study of .
Heat and temperature are NOT the same thing. Heat is a form of that can be transferred from one object to another. Heat flows from to When you hold an ice cube in your hand, your hand feels cold because the heat is
Temperature is a measure of the of all the atoms and molecules in a substance. The higher the kinetic energy, the the molecules move and the temperature
Reactions that are endothermic heat and feel when you touch them. Reactions that are exothermic heat and feel when you touch them.