GenChem q1 module Cheat Sheet (DRAFT) by Jerstellar

Matter - has mass and occupies space.

Atoms have a constant or fixed number of protons
Atomic Number - gives the protons in the nucleus of an atom; repres­ented as Z
Neutral Atom - number of protons is equal to the number of electrons
Z = nuclear charge = number of protons = number of electrons in neutral form
Mass Number - sum of the number of protons and neutrons; repres­ented by A
An atom can be repres­ented by the nuclear symbol ^AzE
Nucleons - protons + neutrons

All atoms of an element have the same mass, although isotopes are atoms of the same element but has different numbers of protons

Ex: All carbons atoms (Z=6) have 6 protons and electrons, but only 98.89% of naturally occuring carbon atoms have 6 neutrons (A=12)

Radica­ls/­Pol­yatomic Ions - stable groups which form chemical bonds as an intact unit.
The valence numbe is taken as one.
If a molecule contains more than one radical (At least two unpaired electr­ons), the formula uses parent­heses. Calcium Phosphate - Ca₃(PO₄)₂

Percentage Compos­ition - amounts of the elements for a given amount of compound
Empirical Formula - simpest formula of any compound (smallest ratio of moles); derived from mass analysis
- Determine the given number of moles in each element
- Divide each by the smallest number of moles given
- Multiply each by the smallest number that will turn them into whole numbers.

Mole(mol) - SI unit for determ­ining molar mass; amount of substance that contains the same number of atoms in 12g of Carbon-12
Avogadro's number - 6.02214076 × 10²³
Elements - mass in amu of 1 atom of an element is the same as the mass in grams of 1 mole of atoms of the element
Mass of S (32.07 amu) is equal to the mass of 1 mol (6.022­14076 × 10²³) of S (32.07 amu)

Law of Conser­vation of Mass - mass is neither created nor destroyed in a chemical reaction
Antoine Lavoisier - French chemist; proponent
Reactants - starting material in a chemical reaction
Product - substance formed in a chemical reaction
Reactants → Products
"to yield" or "to form" (→)
"to react with" or "to combine with" (+)

Stoich­iometry - quanti­tative relati­onship between reactants and products in a chemical reaction
Stoich­iom­etric coeffi­cient - added before an element, ion, or molecule to balance chemical reactions
Mole method using mole-mole factor:
2Na(s) + 2HCl(aq) → 2NaCl(aq) + H₂(g)
2 moles Na ≅ 2 moles NaCl; hence,

3Hg₂(g) + N₂(g) → 2NH₃(g)
How many moles of H₂ are needed to produce 26.5 moles of NH₃?
26.5 moles NH₃ x (3 moles H₂)/(2 moles NH₃) = 39.8 moles of H₂
How many moles of NH₃ will be produced if 33.7 moles of N₂ reacts completely with H₂
33.7 moles of N₂ x (2 moles of NH₃)/(1 mole of N₂) = 67.4 moles of NH₃

2LiOH(s) + CO₂(g) → Li₂CO₃(s) + H₂O(l)
How many grams of CO₂ can be absorbed by 236.1 g of LiOH?
236.1g LiOH x (1 mole of LiOH)/(23.95g LiOH) x (1 mole CO₂) /(2 moles LiOH) x (44.01g of CO₂)/ (1 mole CO₂) = 221.1g CO₂

In chemical reactions, the amount of reactants isn't always stoich­iom­etr­ically exact, so scientists use cheaper reactants (excess)
Limiting Reagent - Reagent that is completely reacted or used up
Excess Reagent - Reactant present with higher quantity than what is required to react in a limiting reagent

3H₂ + 2N₂ → 2NH₃
Suppose 6 moles of H₂ was mixed with 4 moles of N₂ . To determine which is the limiting reagent, the amount of NH₃ must be computed given the moles of H₂ and N₂ and the mole-mole factor of the equation

-To determine how much of 4 moles of N₂ is in excess, use mole-mole factor of N₂ and H₂
6 moles of H₂ x (1 mole N₂)/(3 moles H₂) = 2 moles N₂ in excess
-The number of moles of N₂ required to react with 6 moles of H₂ is only 2, thus, 6 moles of N₂ has an excess of 4 moles
6 moles of N₂ - 2 moles of N₂ in 6 moles of H₂ = 4 moles excess N₂

Mg₂Si + 4H₂O → 2Mg(OH)₂ + SiH₄
If we start with 50.0 g of each reactant, how much in grams SiH₄ can be formed?
50g Mg₂Si x (1 mol Mg₂Si)/(76.7 g Mg₂Si) x (1 mol SiH₄)/(1 mol Mg₂Si) x (32.1 g SiH₄)/(1 mol SiH₄) = 20.9 SiH₄
50 g H₂O x (1 mole H₂O)/(18.0 g H₂O) x (1 mol SiH₄)/(4 mol H₂O) x (32.1 g SiH₄)/(1 mol SiH₄) = 22.3 g SiH₄
50g Mg₂Si = 20.9 SiH₄ (Limiting reactant)
50 g H₂O = 22.3 g SiH₄ (Excess reactant)

Percent Yield - ratio of actual yield to the theore­tical yield expressed as a percentage
Percent Yield = (Actual Yield)­/(T­heo­retical Yield) x 100%
Theore­tical Yield - maximu­m/e­xpected amount of product produced from the given amount of reactant
Actual Yield - actual amount of product produced from the given amount of reactant (deter­mined experi­men­tally)

In calcul­ating theore­tical yield, always use the limiting reactant.from the previous example
Mg₂Si + 4H₂O 2Mg(OH)₂ + SiH₄
If 19.87 g SiH₄ is formed, what is the percent yield of the reaction?
50g Mg₂Si = 20.9 SiH₄ (Limiting reactant) = Theore­tical yield
Percent Yield = (Actual Yield)­­/(­T­h­eo­­retical Yield) x 100%
= 19.87 g SiH₄/20.9 SiH₄ x 100% = 94.89%
Percent error = 100% - 98.89% = 5.11%

Pressure - amount of force exerted per unit area
Standard atmosphere (atm) - widely used unit for pressure; 1 atm = 760mmHg
Torr (or mmHg) - milliliter of mercury equal to 1 atmosp­here; named after Italian scientist Evange­lista Torricelli (invented barometer)
Pounds per square inch (psi) - amount of pressure in pounds that gas exerts in a container per square inch of unit area
kilopascal (kPa) - equal to 1000 Pa, modern unit for pressu­re/­default
Conversion Factor:
1 atm = 760mmHg = 760 Torr = 101.3 kPa = 14.7 psi = 1k Pa = 1000 Pa

Different gases can be present in a container and can be repres­ented as n₁ (gas 1), n₂ (gas 2), or n₃ (gas 3), etc.; the total number of moles as nₜₒₜₐₗ
The pressure exerted by the mixture can be interp­reted as Pₘᵢₓₜᵤᵣₑ = (nₜₒₜₐ­ₗRT)/V
It can be simplified as P₁= (n₁RT)/V; P₂ = (n₂RT)/V; P₃ = (n₃RT)/V
Pressures P₁, P₂, and P₃ are partial pressure of each gas
Dalton's Law of Partial Pressure - pressure exerted by the mixture is the sum of the pressures exerted by each component
Get the partial pressure of gas 1 by P₁ = Pₘᵢₓₜᵤᵣₑ X₁ (wherein X₁ is the mole fraction of gas 1)

Stoich­iom­etric ratio - dictates the ratio of components to start the reaction
Standart Temper­ature and Pressure (STP) = 0°C (273 K) and pressure of 1 atm
Amount of gaseous products are determined using n = (PVₛₜₚ­)/(RT) wherein Vₛₜₚ is the volume of gases involved measured in STP in liters (L)
n = (PVₛₜₚ­)/(­0.0­821­)(273 K) = Vₛₜₚ/22.4
n = Vₛₜₚ/22.4
Gases are also measured in Standard Ambient Temper­ature and Pressure (SATP) which is more accurate than STP which is at 25°C (298 K) and 1 atm.
n = (PVₛₐₜ­ₚ)/­(0.0­82­1)(298 K) = Vₛₐₜₚ/24.5
n = Vₛₐₜₚ/24.5

1. Gases are very small molecules separated by expansive space between them
2. Force of attraction between particles is negligible
3. The molcules are in constant motion and move randomly in all directions
4. Sometimes particles collide with each other or with the walls of container
5. The collisions are perfectly elastic, hence, there is no change in momentum
6. The average kinetic energy is determined only by the absolute tempar­ature of the gas

To determine the kinetic energy of gas particles, the root-m­ean­-square velocity is used:
vᵣₘₛ = √(3RT/M)
where R = ideal gas constant, T = absolute temper­ature in K, M = molar mass in g/mol

To compare the velocities of gases with different molar masses at the same absolute temper­ature:
vᵣₘₛ₁/­vᵣₘₛ₂ = √(M₂)/­√(M₁)
where M₁ or M₂ = molar mass of gas 1 or 2

This expression is also known as Graham's Law of Diffusion which states that the diffusion rate (rate at which the gas moves), is inversely propor­tional to the square root of its molar mass