Reactions and Stoichiometry

Question 1

What is molar mass?

Answer 1

the mass of 1 mole of a species
g/mol
calculate by adding up the molecular weight of the atoms in a species (compound/molecule)

Question 2

How do you calculate empirical formula?

Answer 2

using percentage = imagine 100g of compound, use percentages given to find the grams of each element. Divide each by the smallest value
using molecular formula = divide by the smallest subscript to find ratio

Question 3

What is percent composition by mass?

Answer 3

How much of an atom (by mass) is the compound composed of
find by using the mass number. Take mass contributed to the compound of the atom, divide it by the total mass of the compound x 100 = percent contributed to that compound for the given atom

Question 4

What are the seven reaction types/classes for chemical reactions?

Answer 4

synthesis
decomposition
single displacement
double displacement
neutralization
combustion
oxidation-reduction (redox)

Question 5

Synthesis Reactions

Answer 5

aka combination reaction
two or more reactants combine to form a single product
typically exothermic (making bonds releases energy)
ex:
3 H2 + N2 –> 2 NH3

Question 6

Decomposition Reactions

Answer 6

opposite of synthesis
breakdown of one reactant into multiple smaller products
typically endothermic (takes energy to do)
Ex: 2 KClO3 –> 2 KCl + 3 O2

Question 7

Displacement Reactions

Answer 7

aka replacement
at least one element or group replaces another within a compound
just one = single
two = double, the elements trade places
Ex single:
2 K (s) + 2ZnCl2 (aq) –> 2 KCl (s) + Zn (s)
typically the species that trade places are metal with a halogens, or halogens can displace other halogens
Ex double:
BaCl2 (aq) + MgSO4 (aq) –> BaSO4 (s) + MgCl2 (aq)
typically metals or halogens trading places, but usually the reactants are both ionic compound and the ions are switching places in each to create new products, usually one of them being a solid

Question 8

Neutralization

Answer 8

acid and base react to product a salt and water
you can think of each proton of the acids being canceled out (neutralized) with a hydroxide ion from the base –> aka they form water
don’t always result in a solution of neutral pH, because resulting salt could be acidic or basic
Ex:
HCl (aq) + NaOH (aq) –> NaCl (aq) + H2O (l)

Question 9

Combustion Reactions

Answer 9

when a hydrocarbon reacts with water to product carbon dioxide, water, and heat
it does require just a little heat to get going, but overall reaction is highly exothermic (b/c duh)

Question 10

Oxidation Reduction (redox) reactions

Answer 10

when electrons are transferred from one species to another. The one losing is oxidized, the one gaining is reduced

Question 11

Trick for balancing reactions

Answer 11

start with the element present in the fewest compounds, so whatever element is only in one of the reactants, balance that one first and then go from there

Question 12

How do you find limiting reagent?

Answer 12

1. make sure your equation is balanced
2. calculate the number of moles of each reactant you have
3. Determine how much product you could make with each reactant, assuming the other is in excess
4. Whatever forms the least amount of product is the limiting reactant

Question 13

Calculating percent yield

Answer 13

percent yield = actual mass of desired product/ theoretic mass of desired product x 100%
to get actual mass of product, you have to make sure you’re using the reactant mass, converting to moles, figuring out how many moles of product produced, and then calculating actual mass