Introduction to Chemical
Reactions
Conservation of Mass
If you add two substances together
sometimes you get a chemical reaction.
This is when a new substance is made.
It is very difficult to reverse the reaction and
get the original substances back.
Signs that a chemical reaction has taken
place include a change in colour, heat being
given off or bubbles of gas being made.
Adding acid to
alkali
Fireworks

Ice cream
melting
x

Driving a car

Boiling the kettle
x
frying an egg

Discuss in pairs which of
The changes that are not

these arex chemical reactions
x
chemical changes are called
Lighting a matchphysical changes
Burning a candle

Printing
x
Melting
candle wax
Dissolving sugar
in tea
Making
ice cubes
Ironing
clothes
x
x
Baking a cake
Launching
a space
rocket


Instructions – Closed System
1.
2.
3.
4.
5.
6.
Measure about 30mL of vinegar (acetic acid) into a small
Erlenmeyer flask.
Using your scoopula, place a small amount of baking soda into
your balloon.
Carefully place the balloon over the mouth of the flask making
sure the baking soda does not fall into the flask YET.
Using a balance, measure and record the total mass of the
assembly.
Tip the balloon up and empty its contents into the flask – make
sure your balloon does not come off. Record your observations.
Once the reaction has stopped, measure and record the mass of
the assembly again.
• Questions
1. What evidence of a chemical change did you
notice?
2. Compare the total mass of the Erlenmeyer
flask/balloon assembly before and after the
reaction. What do you notice?
Investigation 1: Open System
1.
2.
3.
4.
5.
6.
7.
8.
Measure about 30mL of vinegar (acetic acid) into a small
Erlenmeyer flask.
Using your scoopula, place a small amount of baking soda into
your balloon.
Carefully place the balloon over the mouth of the flask making
sure the baking soda does not fall into the flask YET.
Mass your assembly and record.
Remove the balloon from your flask
Empty the baking soda into the flask and record your
observations.
Once the reaction has stopped, record the mass of your balloon
and flask.
Clean your area.
Questions – Open System
• Questions:
1. Compare the total mass of the beaker/test tube
assembly before and after the reaction. What do
you notice?
2. Compare the results of the two experiments.
What do you notice? Explain any difference.
Law of Conservation of Mass
• Total mass of reactants = total mass of products
– Reactant are on the left side of the reaction arrow
– Products are on the right side of the reaction arrow
• Number of atoms in reactants = number of
atoms in products
– Atoms cannot be created nor destroyed in a chemical
reaction.
• All a chemical reaction is, is a rearrangement of
the atoms from reactants to products.
Practice
• Eg. 1
– A solid has a mass of 35g. When it is mixed with a solution, a
chemical reaction occurs. If the total mass of the products is
85g, what was the mass of the original solution?
• Eg. 2
– When a forest fire occurs, the ashes that remain have a much
lower mass than the trees that burned. Does this break the law
of conservation of mass? Why or why not?
• Eg. 3
– Solution A has a mass of 60g. Solution B has a mass of 40g.
When they are mixed, a chemical reaction occurs in which a gas
is produced. If the mass of the final mixture is 85g, what mass
of gas was produced?
Word Equations
• Hydrogen gas is reacted with oxygen gas to
form water vapour.
• Word Equation:
– Hydrogen gas + oxygen gas  water vapour
• Balanced Chemical Equation
– 2H2(g) + O2(g)  2H2O(g)
• Skeleton Equation
– H2(g) + O2(g)  H2O(g)
• When dissolved beryllium chloride reacts with
silver nitrate in water, aqueous beryllium nitrate
and silver chloride powder are made.
Aqueous beryllium chloride + aqueous silver nitrate
 aqueous beryllium nitrate + solid silver chloride.