Chemistry

Chemistry 12

Unit 2 Notes - Equilibrium

Chemistry 12 Unit 2- Equilibrium Notes

It's important to know that many chemical reactions are reversible. That is:

Reactants

→ Products

or

Reactants

← Products

Reactants form Products

Products form Reactants

For example, under certain conditions, one mole of the colourless gas N2O4 will decompose to form two moles of brown NO2 gas:

N2O4

colourless

2 NO2

brown

Under other conditions, you can take 2 moles of brown NO2 gas and change it into one mole of N2O4 gas:

N2O4

colourless

2 NO2

brown

In other words, this reaction, as written may go forward or in reverse, depending on the conditions. If we were to put some N2O4 in a flask, the N2O4 molecules would collide with each other and some of them would break apart to form NO2 .

This process is indicated by the forward reaction:

N2O4

2 NO2

Unit 2 Notes – Equilibrium

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Chemistry 12

Unit 2 Notes - Equilibrium

Once this has happened for awhile, there is a build up of NO2 molecules in the same flask Once in awhile, two NO2 molecules will collide with each other and join to form a molecule of N2O4 !

This process, as you might have guessed is indicated by the reverse reaction:

N2O4

2 NO2

Two things you'll have to realize is that as long as there is N2O4 present, the forward reaction will keep on happening and as long as there is NO2 present, the reverse reaction will keep on happening! Also, you must keep in mind that all these molecules are mixed in the same container! At one particular time a molecule of N2O4 might be breaking up, and at the same time two molecules of NO2 might be joining to form another molecule of N2O4! So here's an important thing to understand:

In any reversible reaction, the forward reaction and the reverse reaction are going on at the same time!

This is sometimes shown with a double arrow:

N2O4

2 NO2

The double arrow means that both the forward and...