1. Exothermic and Endothermic Reactions
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2. Chemical Reactions
All chemical reactions involve bond breaking and bond forming.
Energy is needed to break bonds and released when bonds are formed.
Chemical reactions are accompanied by a change in energy, mainly in the form of heat.
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3. Exothermic and Endothermic Reactions
A reaction in which heat is given out is exothermic.
A reaction in which heat is taken in is endothermic.
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4. Cold and hot packs
How do instant hot and cold packs work?

5. Hot pack Pressing the bottom , the diaphragm breaks.
Calcium chloride dissolves in water and warms it.
The beverage gets warm.

6. Exothermic process Hot pack Energy
Heat flows into the surroundings from the system in an exothermic process.
Energy
Surroundings
Hot pack
Exothermic Process comes from the Chemical energy stored in the substances that are reacting (Reactants)
Temperature rises

7. Cold pack
Water and ammonium nitrate are kept in separate compartments.
Pressing the wrapper, the ammonium nitrate dissolves in water and absorbs heat.
The pack becomes cold.
It is used to treat
sports injuries.

8. Endothermic process Cold pack Energy
Heat flows into the system from the surroundings in an endothermic process.
Surroundings
Cold pack
Energy
Temperature falls

9. Cold pack
We will repeat the process in a beaker with ammonium nitrate ( 25 g NH4NO3) + water (25 ml) and a thermometer.
We will record the initial temperature of the water and the temperature after the dissolution of the salt.
Observation:
a temperature drop of…….

10. Endothermic and exothermic reactions
Step 1: Energy must be SUPPLIED to break chemical bonds:
Step 2: Energy is RELEASED when new chemical bonds are made:
A reaction is EXOTHERMIC if more energy is RELEASED than SUPPLIED. If more energy is SUPPLIED than is RELEASED then the reaction is ENDOTHERMIC
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11. Changes in State
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12. What is a Fuel???? What do we do with all of these? Petrol
We Burn Them!!!!
What gets released when we
Burn them??
Carbon Dioxide
Petrol
Gas tank
Wood fires
Coal
Peat

13. Definition time!!!
A fuel is a substance that will undergo a chemical reaction in which a large amount of useful energy is produced at a fast but controllable rate. So fuels are the substances that we use to produce heat and/or electricity, and to run engines and motors.
Many fuels consist of compounds of carbon and hydrogen, which are known as hydrocarbons. When hydrocarbons burn in unlimited air, carbon dioxide and water are produced.
A combustion reaction is when a compound is reacted with oxygen to produce carbon dioxide and water. Combustion is commonly called burning and is an exothermic reaction, which means heat is produced.

14. Combustion Equation
fuel (hydrocarbon) + unlimited oxygen  carbon dioxide + water

15. Forming Na+ and Cl- ions from NaCl is an endothermic process
Endothermic process: a change (e.g. a chemical reaction) that requires (or absorbs) heat.
Forming Na+ and Cl- ions from NaCl is an endothermic process
Photosynthesis is an endothermic reaction (requires energy input from sun)
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16. Measuring Heat
reaction
Endothermic reaction, heat taken in & temperature of the substance drops

17. EXOTHERMIC & ENDOTHERMIC REACTIONS
Exothermic process: a change (e.g. a chemical reaction) that releases heat.
Burning fossil fuels is an exothermic reaction
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18. Exothermic reaction, heat given off & temperature of substance rises.
Heat Released
reaction
Exothermic reaction, heat given off & temperature of substance rises.
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19. Some everyday Examples