1. Chemical Reactions

2. Empirical formula The simplest ratio between the atoms.
The formulas for ionic compounds must be written as empirical formulas.
For molecular substances sometimes the ratio between the atoms in a molecule is not in the simplest ratio. When the molecular and empirical formula are different then the molecular formula is a multiple of the empirical formula.

3. DO NOW
Which compound contains a greater % of Oxygen. Justify your answer with a calculation
Li2O, CaO, PbO2

4. All chemical reactions…
have two parts:
Reactants = the substances you start with
Products = the substances you end up with
The reactants will turn into the products.
Reactants → Products

5. Products
Reactants

6. How to Describe a Reaction
A reaction can be described several ways:
#1. In a sentence every item is a word
Copper reacts with chlorine to form copper (II) chloride.
#2. In a word equation some symbols used
Copper + chlorine → copper (II) chloride
#3. In a chemical equation only chemical equations are used
Cu + Cl2 → CuCl2

7. Symbols in Equations (s) after the formula = solid: Fe(s)
(g) after the formula = gas: CO2(g)
(l) after the formula = liquid: H2O(l)
(aq) after the formula = dissolved in water, an aqueous solution: NaCl(aq) is a salt water solution

8. Symbols used in equations
the arrow → separates the reactants from the products (arrow points to products)
Read as: “reacts to form” or yields or produces
The plus sign + means “and”
↑ used after a product indicates a gas has been produced: H2↑
↓ used after a product indicates a solid has been produced: PbI2↓

9. Symbols used in equations
double arrow indicates a reversible reaction (more later)
shows that heat is supplied to the reaction
is used to indicate a catalyst is supplied (in this case, platinum is the catalyst)

10. What is a catalyst?
A substance that speeds up a reaction, without being changed or used up by the reaction.
Enzymes are biological or protein catalysts in your body.

11. The Skeleton Equation
All chemical equations are a description of the reaction.
A skeleton equation uses formulas and symbols to describe a reaction
but doesn’t indicate how many; this means they are NOT balanced

12. Write a skeleton equation for:
Solid iron (III) sulfide reacts with gaseous hydrogen chloride to form iron (III) chloride and hydrogen sulfide gas.
Nitric acid dissolved in water reacts with solid sodium carbonate to form liquid water and carbon dioxide gas and sodium nitrate dissolved in water.

13. Write a skeleton equation for:
Solid iron (III) sulfide reacts with gaseous hydrogen chloride to form iron (III) chloride and hydrogen sulfide gas.
FeS(s) + HCl(g) → FeCl2(s) + H2S(g)
Nitric acid dissolved in water reacts with solid sodium carbonate to form liquid water and carbon dioxide gas and sodium nitrate dissolved in water.
HNO3(aq) + Na2CO3(g) → CO2(g) + H2O(l)

14. Now, read these equations:
Fe(s) + O2(g) → Fe2O3(s)
Cu(s) + AgNO3(aq) → Ag(s) + Cu(NO3)2(aq)
NO2(g) N2(g) + O2(g)

15. ANSWERS TO WORKSHEET
24. Crystal is a hydrate. Heating removes the water of hydration
25 Hydrated crystal is blue
Anhydrous crystal is white
26 The anhydrous compound is pure. The hydrated crystal contains 50% water so it is more expensive (you are paying for water in the bottle!!!) 3 2 1

16. Balanced Chemical Equations
According to the Law of Conservation of Mass: atoms aren’t created or destroyed in a chemical reaction, they are just rearranged.
All the atoms we start with in the reactants we must end up with in the products (meaning: balanced!)
A balanced equation has the same number of each element on both sides of the equation.

17. Rules for balancing:
Assemble the correct formulas for all the reactants and products, using “+” and “→”
Count the number of atoms of each type appearing on both sides
Balance the elements one at a time by adding coefficients (the numbers in front) where you need more - save balancing the H and O until LAST!
(hint: I prefer to save O until the very last)
Double-Check to make sure it is balanced.

18. Never
Never change a subscript to balance an equation (You can only change coefficients)
If you change the subscript (formula) you are describing a different chemical.
H2O is a different compound than H2O2
Never put a coefficient in the middle of a formula; they must go only in the front
2NaCl is okay, but Na2Cl is not.

19. Practice Balancing Examples
_AgNO3 + _Cu → _Cu(NO3)2 + _Ag
_Mg + _N2 → _Mg3N2
_P + _O2 → _P4O10
_Na + _H2O → _H2 + _NaOH
_CH4 + _O2 → _CO2 + _H2O

20. Practice Balancing Examples
2AgNO3 + _Cu → _Cu(NO3)2 + 2Ag
3Mg + _N2 → _Mg3N2
4P + 5O2 → _P4O10
2Na + 2H2O → _H2 + 2NaOH
_CH4 + 2O2 _CO2 + 2H2O

21. Types of Reactions How? We recognize them by their reactants
There are probably millions of reactions.
We can’t remember them all, but luckily they will fall into several categories.
We will learn: a) the 5 major types.
We will be able to: b) predict the products.
For some, we will be able to: c) predict whether or not they will happen at all.
How? We recognize them by their reactants

22. also called Combination Reactions The general equation is A + B  AB
Synthesis Reaction
also called Combination Reactions
2 substances combine to make one compound A B A B +
The general equation is A + B  AB

23. also called Combination Reactions
#1 Synthesis Reactions
also called Combination Reactions
2 substances combine to make one compound
the general equation is : A + B → AB
Ca + O2 → CaO element + element
SO2 + O2 → SO3 compound + element
CO2 + H2O → H2CO3 compound + compound
We can predict the products, especially if the reactants are two elements.
Mg + N2 → _______
Mg3N2

24. HCl(g) + NH3(g)  NH4Cl(s)
Synthesis Reaction
HCl(g) + NH3(g)  NH4Cl(s)

25. Complete and balance: Ca + Cl2 →
Fe + O2 → (assume iron (II) oxide is the product)
Al + O2 →
Remember that the first step is to write the correct formulas – you can still change the subscripts at this point, but not later while balancing!
Then balance by changing the coefficients only

26. The general equation is : AB → A + B
Decomposition Reaction A B A B +
The general equation is : AB → A + B
A reaction where a more complex molecule breaks down to form two or more simpler products

27. 2NH4NO3(s)  4H2O(g) + 2N2(g) + O2(g) + energy
Decomposition Reaction
2NH4NO3(s)  4H2O(g) + 2N2(g) + O2(g) + energy
Timothy McVeigh bombing, 1995
Regular building demolition with ammonium nitrate explosives

28. #2 - Decomposition Reactions
one reactant breaks apart into two or more elements or compounds.
the general equation is : AB → A + B
H2O H2 + O2
CaCO CaO + CO2
CuSO4•5H2O CuSO4 + 5H2O
2NaHCO3(s) Na2CO3(s) + H2O(l) + CO2(g)
Note that energy (heat, sunlight, electricity, etc.) is usually required

29. #2 - Decomposition Reactions
We can predict the products if it is a binary compound (which means it is made up of only two elements)
It breaks apart into the elements:
H2O
HgO
mercury
mercury (II) oxide
cinnabar

30. Single Displacement Reaction+ B C
A + BC  AC + B
A reaction where an element displaces another element in a compound, producing a new compound and an element
A metal will replace a cation (metal or H)
A non-metal will replace an anion (non-metal)

31. Zn(s) + 2 HCl (aq) → ZnCl2 (aq) + H2 (g)
zinc metal and hydrochloric acid react to form zinc chloride and hydrogen gas in this single-displacement reaction.

32. #3 - Single Displacement Reactions
One element replaces another
the reaction follows the form of: compound + element → compound + element
Reactants must be an element and a compound.
Products will be a different element and a different compound.
Na + KCl → K + NaCl (cations switched)
F2 + LiCl → LiF + Cl2 (anions switched)

33. #3 Single Displacement Reactions
               
#3 Single Displacement Reactions
Metals will replace other metals (and they can also replace hydrogen)
Zn(s) HCl (aq) → ZnCl2 (aq) + H2 (g)
Cu(s) + 2AgNO3 → 2Ag(s) + Cu(NO3)2
Think of water as: HOH
Metals replace the first H, and then combines with the hydroxide (OH).
2Na (s) + 2H2O(l) → 2 NaOH(aq) + H2(g)

34. #3 Single Displacement Reactions
We can even tell whether or not a single displacement reaction will happen:
More ‘active’ element replaces less active
The Activity Series of Metals lists metals (and hydrogen) in order of activity.
Elements higher on the list replaces those lower on the list.

35. Single Displacement Reaction
Hg(NO3)2(aq) + 2Ag(s)  Hg(s) + 2AgNO3(aq)
Will this reaction occur?
H2(g) + ZnCl2(aq)  2HCl(aq) + Zn(s)
What about this reaction?
Both of these reactions do not occur.

36. The “Activity Series” of Halogens
Higher Activity
Halogens can replace other
halogens in compounds, provided they are above the halogen they are trying to replace in the periodic table.
Fluorine
Chlorine
Bromine
Iodine
Lower Activity
2NaCl(s) + F2(g) 
2NaF(s) + Cl2(g)
???
MgCl2(s) + Br2(g) 
No Reaction!
???

37. #3 Single Replacement Reactions Practice:
Fe + CuSO4 →
Pb + KCl →
Al + HCl →

38. Double Displacement Reaction
AD + BC  AC + BD + B C A D
Two compounds switch parts to make two new compounds
the general equation is : AB + CD → AD + CB

39. Double Displacement Reaction
sodium chloride and silver fluoride react to form sodium fluoride and silver chloride in this double displacement reaction

40. #4 - Double Replacement Reactions
Two compounds switch parts to make two new compounds
the reaction is:
compound + compound → compound + compound
NaOH + FeCl3 →
The positive ions change place.
NaOH + FeCl3 →→ Fe+3 OH- + Na+1 Cl-1
= NaOH + FeCl3 →→ Fe(OH)3 + NaCl

41. Double Displacement Reaction
Pb(NO3)2(aq) + 2KI(aq)  PbI2(s) + 2KNO3(aq)

42. #4 - Double Replacement Reactions
Have certain “driving forces”, or reasons
Will only happen if one of the products:
a) doesn’t dissolve in water and forms a solid (a “precipitate”), or
b) is a gas that bubbles out, or
c) is a molecular compound (which will usually be water).

43. Complete and balance:
assume all of the following reactions actually take place:
CaCl2 + NaOH →
CuCl2 + K2S →
KOH + Fe(NO3)3 →
(NH4)2SO4 + BaF2 →
NaOH(aq) + HCl(aq) → H2O(l) + NaCl(aq)

44. How to recognize which type?
Look at the reactants:
E + E OR C + C = Synthesis
C = Decomposition
E + C = Single displacement
C + C = Double displacement

45. Practice Examples: H2 + O2 → → H2O → → Zn + H2SO4 → → HgO → →
KBr + Cl2 → →
AgNO3 + NaCl → →
Mg(OH)2 + H2SO3 →→

46. + fuel O2 Combustion Reaction XyOz + energy
A reaction of a fuel with oxygen, releasing energy in the form of heat and/or light

47. Combustion Reaction

48. Element + O2  “oxide” + energy
Combustion Reaction
Element + O2  “oxide” + energy
2Mg(s) + O2(g)  2MgO(s) + energy
P4(s) + 5O2(g)  P4O10(g) + energy

49. #5 – Combustion Reactions
Combustion is a fast reaction of a substance with oxygen to make compounds called oxides.
the general equation is :
fuel + oxygen → oxides + energy
the three things that must be present for combustion to happen are:
fuel
oxygen
spark / heat

50. Combustion Reaction Examples:
What is the main purpose for which fuels are burned around the world?
The following equations show what happens when different carbon-based fuels are burned.
C(s) + O2(g) → CO2(g) + energy
CH4(g) + 2O2(g) → CO2(g) + 2H2O + energy
ethanol CH3CH2OH(l) + O2(g) → CO2(g) + 3H2O(l)
C6H12O6(s) + 6O2(g) → 6CO2(g) + 6H2O(g) + energy

51. Combustion of other Fuels
Some fuels do not contain carbon.
The products are oxides of each element in the fuels.
Mg(s) + O2(g) → MgO(s)
Cu(s) + O2(g) → CuO(s)
H2(g) + O2(g) → H2O(l)
P4(s) + 5O2(g) → P4O10(g)
S(s) + O2(g) → SO2(g)
As you see, many combustion reactions may also be classified as synthesis.

52. SUMMARY: An equation... Describes a reaction
Must be balanced in order to follow the Law of Conservation of Mass
Can only be balanced by changing the coefficients.
Has special symbols to indicate the physical state, if a catalyst or energy is required, etc.

53. Reactions Come in 5 major types.
We can tell what type they are by looking at the reactants.
Single Replacement happens based on the Activity Series
Double Replacement happens if one product is: 1) a precipitate (an insoluble solid), 2) water (a molecular compound), or 3) a gas.