CHE201: Exam 4 (7.4 - 8) & Chapter 9

Stochiometric amounts

Relative amounts of reactants & products represented in a balanced chemical equation

Limiting reactant

A reactant that is totally consumed during a chemical reaction, limits the extent of the reaction, and determines the amount of product.

Approach for determining limiting reactant

Compare the amount if product expected for the complete reaction of each reactant - the one with the least produced is the limiting reactant

Theoretical yield

Amount of product that may be produced by a reaction, as calculated per the stoichiometry of a balanced chemical equation

Actual yield

Amount of product actually obtained

typically less than theoretical yield

Percent yield

(actual yield / theoretical yield) x 100%

Quantitative chemical analysis

The determination of the amount/concentration of a substance in a sample

Titration

Solution containing a known concentration of one reactant

Analyte

Solution containing a reactant of unknown amount/concentration

Indicator

Added to analyte solution to impart a change in color at/very close to the equivalence point of titration

Equivalence point

Point where enough tirtrant is added in order to complete react with the analyte

End point

Volume of titrant actually measured for expected stoichiometric equivalence

Gravimetric analysis

Type of analysis which a sample is subjected ti sine treatment that causes a change in the physical state of the analyte that permits separation from other component in the sample

commonly via a precipitation reaction

Combustion analysis

Elemental composition of hydrocarbons & related compounds can be determined via this gravimetric method

Barometer

Device used to measure atmospheric pressure

Manometer

Measures pressure of a sample

Amaton's law / gay-lussac's law

P1 / T1 = P2 / T2

Pressure & temperature are proportional

Charles' law

V1 / T1 = V2 / T2

Volume & temperature are proportional

Boyle's law

P1 x V1 = P2 x V2

Pressure & volume are inversely proportional

Avogadro's law

V1 / n1 = v2 / n2

Volume & moles are proportional

Ideal gas law

PV = nRT

* R = 0.08206

* Can be used to express density of a gas using pressure / temp, etc.

Dalton's law of partial pressures

Ptotal = P1 + P2 + P3...

Diffusion

Process which gas molecules disperse in open space

Effusion

Gas molecules must move through an extremely small space (pin hole)

Graham's law of effusion

rate of effusion is proportional to 1 / sqrt(mass of gas particles)

Kinetic-Molecular Theory (KMT)

1. Gases are composed of molecules in continuous motion, traveling straight & only changing direction when they collide

2. The molecules are negligibly small compared to the distance between them

3. Pressure causes collisions between gas molecules & container

4. Gas molecules exert no repulsive/attractive force on each other

5. Average KE is proportional to temperature of gas

Properties of an ideal gas

- Temperature is high

- Pressure is low

- Gas molecules are small

- Gas molecules have no dipole

- Fewer moles of gas

Thermochemistry

Heat absorbed/released during chemical & physical change

Energy

Capacity to supply heat / do work

Work (w)

Process of causing matter to move against a force

Kinetic energy

Energy of motion

Potential energy

Energy by position

Law of conservation of energy

Energy can only be transferred and cannot be created

Thermal energy

Kinetic energy due to the motion of atoms

Temperature

Quantitative measure of how “hot” / “cold” something is

Heat (q)

Transfer of thermal energy

Exothermic

Releases heat (A —> B + heat)

ΔH < 0

Endothermic

Absorbs heat (A + heat —> B)

ΔH > 0

Calorimetry

Measures the heat

First law of thermodynamics

Total energy of an isolated system is constant & energy can only be transferred

State function (u)

Only depends on the beginning & end state of the matter

Standard state (ΔH°)

1 bar & 1 molar concentration (1 atm = 1 bar) & room temp = 25°C / 298.15 K

Hess’s Law

If a process can be written as the sum of several stepwise processes, enthalpy change of total process is the sum of the enthalpy changes of the various steps

Bond breaking

Endothermic - requires energy

Bond forming

Exothermic - releases energy

Bond strength

Covalent bonds