1. Chemical Reactions
Topic 5 Semester 2

3. Introduction to Chemical Reactions
Chemical equations spell out what happens during a reaction.
Chemical reactions are generally noted by;
The appearance of a gas or bubbles
A color change in the mixture
A precipitate appearing or disappearing
Temperature change of the mixture

4. Word Chemical Equations
description of a chemical reaction using words
magnesium + oxygen  magnesium oxide
(reactants)  (product)

5. From word equations to standard chemical equations
Using your periodic table and ion chart try and write the chemical equations for each of the following word equations. Use a QR scanner to check your answer.
Remember: There are 7 diatomic elements meaning that these elements will always come in a pair in an equation. Watch the video to learn more about diatomic elements.
Please note some compounds come with prefixes such as:
Mono = 1 Di = 2 Tri = 3 Tetra = 4 Penta = 5
Iron + Chlorine gas
 Ferric Chloride
Hydrogen gas + oxygen gas
 dihydrogen monoxide
Magnesium + dihydrogen monoxide
 magnesium hydroxide + hydrogen gas

6. Skeleton Equations and Balanced Equations
Skeleton Equations show just the formulas and are not necessarily complete.
Word eq: magnesium + oxygen  magnesium oxide
Skeleton eq: Mg O2  MgO______
What is not complete about this skeleton equation? Its not balanced!
Balanced equations are necessary to show exactly how many of each reactant or molecule is needed.
Balanced eq: 2Mg O2  MgO______

7. Anatomy of a Reaction equation
2H2(g) + O2(g) → 2H2O(l)
|_____Reactants_____| |__Products__|
Phases of Matter
g = Gas
l = Liquid
s = Solid
Aq = aqueous (dissolved in water)
Coefficients

8. Tips for Balancing Equations
Use an eraser. You WILL make mistakes. (that’s ok)
Consider writing down the # of each atom as you go. You can even draw atoms if that helps.

9. Tips for Balancing Equations
Don’t give up! Sometimes starting with a different atom can help. (If an element is by itself, try it last!)
(There is one SO4 group on both sides.)
If a polyatomic ion (like NH4 or CO3) appears on both sides, balance together as a group instead of separate atoms.

10. Tips for Balancing Equations
Never change subscripts to get formulas to balance. Can’t you just get rid of the 2? No! Only ever add coefficients.

11. Why is balancing important?

12. Practice Balancing
Go to the simulation above and balance each of the 3 equations. Show Ms. Cobler your answers.

13. Practice Balancing Copy the following equations into your notebook and Balance each equation. Show Ms. Cobler your answers.
HgO (s)  Hg (s) + O2 (g)
Na (s) + H20 (g)  NaOH (s)+ H2 (g)  
ZnS (s) + O2 (g)  ZnO (s) + SO2 (g)
 SO3 (g) + H20 (g)  H2SO4 (l)
 CaCO3 (s)+ HCl (l)  CaCl2 (s) + CO2 (g) H20 (g)
 O2 (g) + N2 (g)  NO2 (g) . 
Fe (s) + F2 (g)  FeF3 (s)

14. https://www. youtube. com/watch

15. General formula and Organization A + B  AB
Combination Reaction
Is also referred to as a synthesis reaction
It is a chemical change in which two or more substances react to form a new singular substance
The product is a compound in this form of reaction
You can tell this reaction has occurred because on the reactant side there are multiple substances, while on the product side there is only one product
General formula and Organization
A + B  AB

16. 1. Synthesis (combination) reactions
A + B → AB
Two or more atoms or small molecules come together to make a larger molecule.
2H2 + O2 → 2H2O

17. Decomposition Reaction
This is a chemical change where a single compound (the
reactant) breaks down into two or more simpler products.
This type of reaction is easily identifiable, because:
It is the exact opposite of synthesis; if you know one you know them both
There is always one reactant. If you see one reactant that’s a compound and several products, a decomposition reaction occurred.
General formula and Organization

18. 2. Decomposition reactions
AB → A + B
A large molecule breaks into smaller molecules or atoms.
2 Hg(SCN)2 →
2 HgS + C3N4 + CS2

19. Single Replacement Reaction
A chemical change where one element replaces a
second element in a compound.
It is identifiable by its symmetry. On the reactant side there is a single element and a compound, as there is on the product side.
No reaction will occur if the most reactive element is already in the compound
General formula and Organization
AB + C  AC +B

20. 3. Single replacement reactions
A + BX → AX + B
One atom or ion takes the place of another in a compound.
Like atoms replace like atoms. Like ions replace like ions. (Never put + ions with + or - with -)
F2 + 2NaCl → Cl2 + 2NaF
Fe + CuSO4 → Cu + FeSO4

21. Double Replacement Reaction
A chemical change where there is an exchange of positive ions between two compounds
May also be called double-displacement reactions
Generally take place in aqueous solution
Often produce a precipitate, a gas, or a molecular compound (i.e. water)
General formula and Organization
AB + CD  AC + BD

22. 4. Double replacement reactions
AB + CD → AD + CB
Atoms or ions exchange partners.
Ions always switch so + goes with -, never two +’s or –’s together.
NaCl + AgNO3→
NaNO3 + AgCl (s)

23. Double Replacement Reaction
A chemical change where an element or a compound, generally a carbohydrate (compound made up of carbons, hydrogens, oxygens, and occasionally other elements) reacts with oxygen
This will often yield energy in the form of heat and light
Oxygen is ALWAYS going to be on the reactant side
This is the main indicator that a combustion reaction has occurred is the presence of Carbon dioxide and water.
General formula and Organization
CxHy + O2  CO2 + H2O

24. 5. Combustion reactions X + O2 → XO
Always a rapid reaction with oxygen gas.
Produces oxides.
CH4 + 2O2 → CO2 + 2H2O

25. Classifying reactions

26. Complete the Chemical Equations: Balancing & Classifying worksheet
Ask Ms. Cobler for this worksheet.

27. Predicting Products
Now using what you know about the 5 main types of chemical equations, your ion sheets, and your periodic tables. You can start predicting the products of reactions. We will not worry about Acid-Base reactions right now.
Watch this video then continue on:

29. Complete the Predicting Products of Reactions worksheet
Ask Ms. Cobler for this worksheet.