CHEMICAL ENERGETICS

CHAPTER 8: CHEMICAL ENERGETICS

Chemical & Energy

Chemicals

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Energy

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AB + C = AC + B

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When chemical reaction takes place

Energy is being absorbed/released

energy & chemical reaction

Lets sketch how energy is being absorbed and released during a chemical reaction..

pens and paper..

Energy will start to transfer to or from the environment (surrounding)?

When chemical reaction takes place and energy is released to the environment

the process is called..

EXOTHERMIC

EXIT

When chemical reaction takes place and energy is absorbed from the environment

it is called

ENDOTHERMIC

ENTER

HOW CAN WE REPRESENT ENERGY COMING IN AND GOING OUT??

ENERGY LEVEL DIAGRAM

ENERGY LEVEL DIAGRAM

A diagram showing the energy change of the reaction on vertical axis and the reactants and products on the horizontal axis.

WHY IS THERE ENERGY CHANGE?

What is happening in a chemical reaction??

Lets draw the energy level diagram

IMPORTANT!!!!

Lets recap

exo & endo

EXOTHERMIC (EXIT)

• Gives out energy

• Surrounding temperature rise/increase

• The reaction can be described as: reactants = products + energy

• formation of new bonds

EXOTHERMIC (eg:)

• combustion of fuels (O₂ + gas)

• neutralization (acid + base)

• respiration in our body

ENDOTHERMIC(ENTER)

• Take in energy from the surrounding

• Surrounding temperature fall

• The reaction can be described as: reactant + energy = products

• Since energy is absorbed products must have higher energy than reactants.

• Bonds breaking

ENDOTHERMIC (eg)

• reactions that take place in cooking

• photosynthesis: plants absorbed sunlight energy to convert CO_{2 +} H₂O = Glucose

• ice melting

9.2

MAKING & BREAKING BONDS

MAKING & BREAKING BONDS

In a chemical reactions, bonds must first be broken. Then new bonds form. Breaking bonds takes in energy. Making bonds releases energy.

BOND ENERGIES

...is the energy needed to make or break bonds.

Energy needed (enter) to break bonds. (Endothermic = absorbed)

Energy given out (exit) when making bonds (Exothermic = released)

Bond energy = (kJ/mole)

units

BOND ENERGY CALCULATION

• Each chemical bond has a specific bond energy

• This is the amount of energy require to break or form the bond

• This energy can be used to calculate how much heat would be released or absorbed in a reaction

• Identify bond present in reactants & products

LETS DO CALCULATION

CALCULATOR!!