1. Chemical Reactions & Equations

2. Goals Observe Physical Changes associated with a Chemical Reaction
Give evidence of the occurrence of a chemical reaction
Write a balanced equation for a chemical reaction
Identify the type of reaction

3. How do we know when a reaction occurs?
Bubbles/fizzing (liquid  gas)
Precipitation (solution goes cloudy and you see a ‘rain’ of solid particles falling to the bottom of the test tube)
A change in the color of the mixture
The solution gets hotter or colder
Disappearance of a solid
You see light given off

4. Balancing a Chemical Reaction
In a reaction there are
reactants (what we start with)
products (what we end up with)
In a chemical equation we write
reactants  products
A chemical equation needs to be balanced so that the same number of each type of atom are present on both sides
To balance a reaction we write a number called a coefficient in front of the chemical formula for a reactant or product

5. Balancing a Chemical Reaction
Nitrogen gas and Hydrogen gas react to make Ammonia
N2(g) + H2(g)  NH3(g) (unbalanced reaction)
There are 2 N on the left
But only 1 N on the right
So we put a 2 in front of the NH3
N2(g) + H2(g)  2NH3(g) (the 2 balances the N atoms)
But what about the H? (there are 2 on the left and 6=2x3 on the right)
N2(g) + 3H2(g)  2NH3(g) (the 3 balances the H atoms)

6. Types of Reaction Type of Reaction Description Example Equation
Combination
Elements or compounds combine to make a more complex product
Cu + S  CuS
Decomposition
A reactant falls apart into simpler fragments
CaCO3  CaO + CO2
Single Replacement
One element takes the place of another element in a compound
Mg + 2HCl  MgCl2 + H2
Double Replacement
Elements in two compounds swap places
AgNO3 + NaCl  NaNO3 + AgCl
Combustion
Reactant and oxygen form oxides
S + O2  SO2

7. A. Magnesium and Oxygen
Burn a 2-3 cm strip of Magnesium ribbon in a bunsen
Use tongs to hold the Magnesium in the flame and wear goggles
Write down your observations of the reaction and products
Balance the reaction ____Mg(s) + _____O2(g)  _____ MgO(s)
What type of reaction is this?

8. B. Zinc and Copper (II) Sulfate
Pour 3 mL of Copper (II) sulfate into 2 identical test tubes
Place a small piece of Zinc in one of the test tubes
Observe the color changes
Initially
After 15 mins
After 30 mins
Balance the Equation
____Zn(s) + ____CuSO4(aq)  ____Cu(s) + ____ZnSO4(aq)
What type of reaction is this?

9. C. Metals and Hydrochloric Acid (HCl)
3 test tubes each with 3 mL of 1M HCl
To one add Copper (Cu)
To one add Zinc (Zn)
To one add Magnesium (Mg)
Observe the reactions
Any evidence of H2(g)? Bubbles? Can you explode the gas?
Does the metal dissolve?
Balance the reactions
___Cu(s) + ___HCl(aq) - ____ CuCl2(aq) + ___H2(g)
___Zn(s) + ___HCl(aq) - ____ ZnCl2(aq) + ___H2(g)
___Mg(s) + ___HCl(aq) - ____ MgCl2(aq) + ___H2(g)
What types of reactions are these?

10. D. Reactions of Ionic Compounds
Reactant 1
Reactant 2
Observations
Balance
CaCl2
Na3PO4
___CaCl2(aq) + ____Na3PO4  ___NaCl(aq) + ___Ca3(PO4)2(s)
BaCl2
Na2SO4
___BaCl2(aq) + ____Na2SO4  ___NaCl(aq) + ___BaSO4(s)
FeCl3
KSCN
___FeCl3(aq) + ____KSCN  ___KCl(aq) + ___Fe(SCN)3(s)
React 20 drops and reactant 1 (in one test tube) with 20 drops of reactant 2 (in a second test tube)
Describe them before they are mixed
Describe them once they are mixed together
Balance the reactions
What type of reactions are these?

11. E. Sodium Carbonate (Na2CO3) with HCl
You are wearing goggles right?
3 mL of 1M HCl in a test tube
Add a small amount of Na2CO3 (sodium carbonate)
Record observations (gasses?)
Place a lit match or wood splint into the neck of the test tube what happens to the flame?
Balance the reaction
Na2CO3(s) + ___ HCl(aq)  ___ CO2(g) + ___ H2O(l) + ___NaCl(aq)
What type of reaction is this?