MATH IN CHEMISTRY

Chemical reactions

Text Book Chapter 10 & 11

CHEMICAL REACTIONS

Chemical Reaction: ______

Reactant(s)  Product(s)

______

* Arrow represents “YIELDS” not equals. ______

______

Counting Atoms

Remember that coefficients (big number in front of a symbol) applies to everything after it, while subscripts(small number after a symbol) applies to everything immediately before it. If a subscript is after a parenthesis, it applies to everything in the parenthesis.

3H2O = ___ H ___ O

Li2SO4 = ___ Li ___ S ___ O

3 Al2O3 = ___ Al ___ O

Ca (C2H3O2)2 = ___ Ca ___ C ___ H ___ O

4 Al2(SO3)3 = ___ Al ___ S ___ O

2 Mg(OH)2 = ___ Mg ___ O ___ H

5 ZnSO4 = ___ Zn ___ S ___ O

BALANCING EQUATIONS

Remember the Law of Conservation of Matter . . . Atoms in a reaction are ______!

Balanced Chemical Equation: ______

______

** All compounds should be written correctly! Remember swap and drop before balancing if it is not done already.

  1. Count how many ______ of each element you have on ______
  1. Only add ______ to the front of the compound to balance the equation!! (______!!!)
  1. Double check each element

MINOH = Metals...(polyatomic) Ions...Nonmetals...Oxygen...Hydrogen

Example: ___Al + ___HCl  ___AlCl3 + ___H2

ReactantProduct

How many Al? ______

How many H? ______

How many Cl? ______

**If there is only 1 of a substance, you can leave the space blank or write a number 1. DO NOT WRITE ZERO

Balancing Equations

1)____ NaF + ____ Br2 ____ NaBr + ____ F2

2)____ MgF2 + ____ Li2CO3 ____ MgCO3 + ____ LiF

3)____ P4 + ____ O2 ____ P2O3

4)____ RbNO3 + ____ BeF2 ____ Be(NO3)2 + ____ RbF

5)____ AgNO3 + ____ Cu  ____ Cu(NO3)2 + ____ Ag

6)____ CF4 + ____ Br2 ____ CBr4 + ____ F2

7)____ HCN + ____ CuSO4 ____ H2SO4 + ____ Cu(CN)2

8)____ GaF3 + ____ Cs  ____ CsF + ____ Ga

9)____ BaS + ____ PtF2 ____ BaF2 + ____ PtS

10)____ N2 + ____ H2 ____ NH3

11)____ Na3PO4 + ____ KOH  ____ NaOH + ____ K3PO4

12)____ Pb(OH)2 + ____ HCl  ____ H2O + ____ PbCl2

13)____ AlBr3 + ____ K2SO4 ____ KBr + ____ Al2(SO4)3

14)____ CH4 + ____ O2 ____ CO2 + ____ H2O

15)____ Na3PO4 + ____ CaCl2 ____ NaCl + ____ Ca3(PO4)2

16)____ K + ____ Cl2 ____ KCl

17)____ Al + ____ HCl  ____ H2 + ____ AlCl3

18)____ N2 + ____ F2 ____ NF3

19)____ SO2 + ____ Li2Se  ____ SSe2 + ____ Li2O

20)____ NH3 + ____ H2SO4 ____ (NH4)2SO4

IDENTIFYING TYPES OF REACTIONS

Possible indications of a chemical reaction occurring:

  1. ______
  2. ______
  3. ______
  4. ______
  5. ______

Chemical reactions can be grouped into 4 basic types (there are more!)

  1. Synthesis: A + B  AB

______

Example:

  1. Decomposition: AB  A + B

______

Example:

  1. Single Replacement: AB + C  CB + A

______

Example:

  1. Double Replacement: AB + CD  AD + CB

______

Example:

General tips for writing skeleton equations

  1. ______
  1. ______ (Br, I, N, Cl, H, O, F or 7-up)

If they are by themselves (not in a compound) add the subscript

  1. Identify any polyatomic ions (______)

Write them ______ as they are in Table E. NEVER CHANGE THEM!!

  1. ______
  1. ______ charges. (Remember to use the first oxidation state listed, unless the metal has more than 1 number listed, then determine which number was used)
  1. Only use ______ to balance the equation

Magnesium plus oxygen yields magnesium oxide

MOLES

Mole = Avogadro’s number

A mole is a unit of measurement – it is an amount of items.

1 pair = ______items

1 dozen = ______items

1 gross = ______items

1 ream = ______items

1 mole = ______items

Some examples of a mole of items:

“items” can be anything, including particles!

Atomic mass units are too small to measure on a laboratory balance, but grams are not. So we can group atoms/molecules together until there are so many of them that we can measure them on our classroom scale.

GRAM FORMULA MASS

1 mole of any element = its’ formula mass in grams

Knowing this, we can now convert from moles to grams and from grams to moles!

MOLE CONVERSIONS

EQUALITY STATEMENTS

1 mole = gram formula mass (gfm)

1 mole = 6.02 x 1023 things (particles, atoms...)

1 Mole = 22.4 Liters (ONLY IF GAS @ STP)

DIMENSIONAL ANALYSIS:

  1. Start with the number and units you are given (which can be over 1)
  2. MULTIPLY this by a conversion factor
  3. Put the units you want on the top, and the units you started with on the bottom
  4. Fill in the conversion factor with the equality statement
  5. Remember to MULTIPLY across (not cross multiply)

Number units you are givenX ___units you want___then fill in

1 units you started withequality

statement!

______

DIMO = Divide In Multiply Out

If you are given mass and need to find moles, DIVIDE into moles by the gfm

If you are given moles and need to find mass, MULTIPLY out by the gfm

If you are given # of molecules & need to find moles, DIVIDE by 6.02 x 1023

If you are given moles & need to find # molecules, MULTIPLY by 6.02 x 1023

If you are given volume of a gas @ STP & need to find moles, DIVIDE by 22.4

If you are given moles and need to volume of a gas, MULTIPLY out by 22.4

FIND MASS FROM MOLES

  1. What is the mass of 3 moles of potassium nitrate (KNO3)?
  1. What is the mass of 0.75 moles of aluminum oxide [Al2O3]?

FIND MOLES FROM MASS

  1. How many moles are in 484.25g of ammonium phosphate [(NH4)3PO4]?
  1. How many moles are in 543 g of tin IV fluoride [SnF4]?

FIND # MOLECULES FROM MOLES

  1. How many molecules are in 2 moles of water?
  1. How many molecules are in 38 moles of glucose?

FIND MOLES FROM # MOLECULES

  1. How many moles of ammonia are 2.8 x 1024 molecules?
  1. How many moles of sucrose [C12H22O11] are 6.8 x 1023 molecules?

FIND VOLUME OF GAS FROM MOLES

  1. What is the volume of 25 moles of Ne at STP?

FIND MOLES FROM VOLUME OF GAS

  1. How many moles of H2will occupy 50 liters?

MOLES ↔MASS CONVERSIONS

1)How many grams are in 4.5 moles of sodium fluoride, NaF?

2)How many moles are in 98.3 grams of aluminum hydroxide, Al(OH)3?

3)How many grams are in 0.02 moles of beryllium iodide, BeI2?

4)How many moles are in 68 grams of copper (II) hydroxide, Cu(OH)2?

5)How many grams are in 3.3 moles of potassium sulfide, K2S?

6)How many moles are in 1.2 x 103 grams of ammonia, NH3?

7)How many grams are in 2.3 x 10-4 moles of calcium phosphate, Ca3(PO3)2?

8)How many moles are in 3.4 x 10-7 grams of silicon dioxide, SiO2?

9)How many grams are in 1.11 moles of manganese sulfate, Mn3(SO4)7?

STOICHIOMETRY

Stoichiometry =calculations based on ______relationships in a balanced chemical equation

The equation for the formation of ammonia, 3H2 (g) + N2 (g) →2NH3(g), tells us that 1 molecule of nitrogen combines with 3 molecules of hydrogen to form 2 molecules of ammonia. This also means 1 moleof nitrogen combines with 3 moles of hydrogen to form 2 moles of ammonia.

Assumptions of stoichiometry:

1. Reaction has no ______

2. The reactants are ______

Mole problems

The coefficients in front of each species lets you know what the proportional number of moles of reactant needed is to make a proportional number of moles of product. For example, in the manufacture of ammonia (called the Haber Process), a simple synthesis reaction is used:

N2 + 3 H2→2 NH3

What this means is that if nitrogen and hydrogen are reacted in a 1:3 mole ratio, the amount of ammonia you will produce from the reaction is 2 moles. This is important to know, because if your company gets a call for 10 moles of ammonia, you can use that 1:3 → 2 proportion to determine how many moles of nitrogen and hydrogen you have to react together in order to make the 10 moles of ammonia.

Let’s see how this scales up: ___ moles N2 + ___ moles H2 →____ moles NH3

This maintains the 1:3 → 2 ratio that the coefficients give you!

What if you needed 34.338 moles of NH3? Is there an easy way to make use of the 1:3 → 2 ratio to figure that out? Of course! Dimensional analysis!

How many moles of H2 is needed to produce 34.338 moles of NH3?

  1. Start with what you know (we are given 34.338 moles of NH3)
  2. Times a line (We need to keep the value the same but change the units, so we multiply this by a conversion factor.)
  3. Desired units on top (we want to find moles of H2)
  4. Given units on the bottom (we started with moles of NH3)
  5. Fill in the numbers from the balanced equation (3 moles of H2 and 2 moles of NH3)
  6. Multiply across, cancel units as possible

MOLE TO MOLE STOICHIOMETRY PRACTICE

1)Given the equation:

4Al (s) + 3O2 (g) → 2Al2O3 (s)

How many moles of Al are needed to form 3.7 moles of Al2O3?

2)Given the equation:

5C (s) + 2SO2 (g) → CS2 (l) + 4CO (g)

a)How many moles of CS2(l) form when 2.7 moles of C (s) react?

b)How many moles of C(s) are needed to react with5.44 moles of SO2(g)?

c)How many moles of CO (g) form at the same time that 2.46 moles of CS (l) form?

d)How many moles of SO2 (g) are required to make 118 moles of CS2(l)?

More Stoichiometry Practice

1) For the reaction N2(g) + H2(g) NH3(g):

a) Balance the reaction:

_____N2(g) + _____H2(g) _____NH3(g)

b) How many moles of N2 are needed to make 5.0 moles of NH3?

c) How many moles of N2 are needed to completely react with 10.0 moles of H2?

d) How many moles of NH3 should form if 6.0 moles of H2 are completely reacted with N2?

2) For the reaction Zn(s) + HBr(aq) ZnBr2(aq) + H2(g)

a) Balance the reaction:

_____Zn(s) + _____HBr(aq) _____ZnBr2(aq) + _____H2(g)

b) How many moles of Zn are needed to make 8.0 moles of ZnBr2?

c) How many moles of HBr are needed to make 4.0 moles of H2?

d) How many moles of ZnBr2 should form if 5.0 moles of HBr are completely reacted with Zn?

3) For the reaction Ca(s) + N2(g) Ca3N2(s)

a) Balance the reaction:

_____Ca(s) + _____N2(g)_____Ca3N2(s)

b) How many moles of Ca are required to form 4.00 moles of Ca3N2?

c) How many moles of Ca3N2 will form if 2.50 moles of N2 are reacted?

d) How many moles of Ca are needed to completely react with 5.00 moles of N2?

4) For the reaction Al + MgCl2AlCl3 + Mg

a) Balance the reaction:

_____Al + _____MgCl2_____AlCl3 + _____Mg

b) How many moles of Mg will be formed if 35.0 moles of Al are reacted?

c) How many moles of MgCl2 are required to completely react with 15.0 moles of Al?

d) How many moles of AlCl3 will be formed if 13.0 moles of Mg are formed?

NAME: ______

Anhydrate

Coefficient

Decomposition

Double replacement

Empirical formula

Gram formula mass

Hydrate

Mole

Molecular formula

Percent composition

Product

Reactant

Single replacement

Stoichiometry

Subscript

Synthesis