Stoichiometry

Question 1

Avogadro’s number

Answer 1

6.022 x 10²³

Question 2

Mole

Answer 2

The number of atoms in a sample that weighs that element’s atomic weight

Question 3

Calculating limiting reactant (when the question does not specify the “excess”

Answer 3

1. Balance the chemical reaction
2. Convert everything to moles
3. Divide: calculated moles / coefficients
4. Smallest one is the limiting reactant
   BCDS

Question 4

Formula for percent yield

Answer 4

Actual yield / theoretical yield x 100%
Actual = amount of product given in the problem
Theoretical = amount of product calculated from the limiting reactant

Question 5

Formula for density

Answer 5

Density = mass / volume

Question 6

An element X forms an oxide X₂O₃ with a mass ratio of 0.50 g X / 1 g O. What is the atomic mass of X?

Answer 6

Question 7

Ammonia is formed according to the reaction: N_2(g) + 3H_2(g) —> 2NH_3(g).
A chemist mixes 28 grams of nitrogen gas and 18 grams of hydrogen gas in a 2.0 L vessel. How many grams of hydrogen gas will be consumed?

Answer 7

Question 8

Chemical reactions

Answer 8

Atoms rearrange their combinations in order to form new substances

Reactants (old bonds break) —> products (new bonds form)

Question 9

Synthesis/combination reaction

Answer 9

Two things become one thing

A + B —> A-B

Question 10

Decomposition reaction

Answer 10

One thing splits up into two things

A-B —> A + B

energy must be supplied to break A-B bond (ex: heat, light)

Question 11

Single displacement reaction

Answer 11

One compound swaps out one component

A-B + C —> A-C + B

Question 12

Double displacement reaction

Answer 12

Two compounds swap components

A-B + C-D —> A-D + C-B

Question 13

Molar mass

Answer 13

Equal to the mass per mole of a substance
Unit: g/mol

Question 14

In order to calculate molar mass, we must know the:

Answer 14

Molecular formula of that specific compound

Question 15

Formula for percent yield:

Answer 15

Percent yield = actual yield / theoretical yield