Flashcards in Chemistry 11 Unit 3 Quantities in Chemical Reactions Deck (10):

1

##
Mole?

Examples

###
Mole: (mol)-used to described an amount of atoms or molecules.

• 1 mole = 6.02 x 10^23

• Referred to Avogadro’s number (NA)

Ex: 12 g of carbon (pencil leads) = 1 mole (atomic mass of an element on the Periodic Table)

-602 earth sized planets covered 1 m deep of peas →large number

-1/8 the surface area of the sun

2

## Important things to remember when doing calculations:

###
-Balance all equations

-units

-proper rounding (final: 2 decimal; other: 3 or more decimal)

-be aware of what the question is asking for

-be aware of numbers (0.0___ on calculator)

3

## Atomic Mass

###
Atomic Mass: (g/mol)- mass of one mole of atoms in an element (mass of an atom)

• Contains 6.02 x 1023 atoms

• Ex: Carbon’s atomic mass is 12 g = 1 mole

• Sum of the protons and neutrons in an atom (because make up majority of atom’s mass) →proton and neutron each have a mass of 1

• Since electrons are extremely light, do not contribute to mass

4

## Molar Mass

###
Molar mass: (g/mol)- mass of one mole of molecules in a compound or substance.

• Contains 6.02 x 1023 molecules.

• Found by adding the atomic masses of atoms making up the molecule/compound

o Ex: water

• 2(H) + 1(O)

• 2(1) + 1(16)

• 18 g/mol

• Mass on the periodic table (ex: 16g is 1 mole for oxygen)

• Do not need to use coefficient (because coefficient is only used for mole ratios)

5

## Mole calculations (n)

###
formulas:

n = V/MV (molar volume at STP: 22.4 L/mol)

n = m/mm

n = #p/Na (avogadro's number in particles)

# of atoms

1) find #p (molecules)

2) multiply #p by subscript of element want to find in the compound

6

## Calculation Reminders

###
-units

-HOFBrINCl

-gas molecules = 2 atoms (Ex: Fluorine gas = F2 with molar mass 2(19) = 38 g/mol)

-write down what is given, need to find

7

## Stoichiometry

###
-requires balanced chemical reaction

-coefficients in front of substances represent # of moles

Mole ratio: (mole of substance you have/coefficient of substance you have)*coefficient of substance you want

Mole to Mole -->using mole ratio

Mass-Mass

Volume-Volume

Particle-Particle

Mixed mass-volume-particle

Energy

8

## Energy Stoichiometry

###
-exothermic (releasing heat, product side)

-endothermic (absorbing heat, reactant side)

1) convert to moles

2) mole ratio x energy coefficient

3) answer above in KJ

Alternative way to solve:

Coefficient of known mole substance : coefficient KJ

mole of known substance : X (unknown)

^solve for X as a ratio

9

## Limiting Reactants

###
Reactant that limits the final yield of products (ex: cheese sandwich analogy)

-occurs when given two masses or two moles

-requires extra step before stoichiometry

-Goal is to determine the LR out of the two reactants (one will be LR one will be excess)

1) take info on reactants and convert to moles

2) box 1:1 ratio

for each reactant:

# of moles/coefficient

-lowest/smallest number of moles is LR

4)use the moles of the LR to solve

To calculate amount of excess left over:

Moles of excess to start - moles of excess used/required (from LR moles/LR coefficient * excess coefficient)

-leftover mols and grams (must convert)

Other ways of saying left over: unreacted, not used, amount left over

10