Chemistry - Gas Laws, Thermodynamics

Charasteristics of Gas

Charasteristics of Gas

Volume, Pressure, Temperature

Units for volume

Litres - L (si unit) dm^3 - decimeter cubed (convenient and used used in IB)

Units for temperature

C - degrees celsius K - kelvin

Celsius to Kelvin formula

K = C + 273.15

What is the lowest temperature possible in K

0 K: absolute zero

Pressure

The force applied over an area (m^2)

Units for pressure

N/m^2 Pa - pascal

Converting pressure units

1.0 atm = 101325 Pa = 101.325 kPa = 1.01325 bar = 760 torr = 760 mmHg = 14.6959 psi

mmHg

Mercury

Standard Temperature and Pressure (STP)

"Standard" set of conditions exactly 273 kPa and 100. kPa

Standard Ambient Temperature and Pressure (SATP)

exactly 298 K and 100 kPa

Gas Laws

• As pressure increases, volume decreases

• As temperature increases, volume increases

• As temperature decreases, pressure decreases

• As temperature increases, pressure increases

As pressure increases, volume decreases

P ∝ 1/V PV = constant

As temperature increases, volume increases

T ∝ V T/V = constant

As temperature decreases, pressure decreases As temperature increases, pressure increases

P ∝ T P/T = constant

Boyle's Law

P1V1=P2V2 @ Constant T

Charlses' law

V1/T1 = V2/T2 @ Constant P

Gay Lussac's Law

P1/T1 = P2/T2 @ Constant V

Combined Gas Laws

P1V1/T1=P2V2/T2 @ constant mols

Units for gas laws

T - always use Kelvin P, V - units do not matter as long as the units are the same on both sides

Avogadro's Law

As you add additional gas to a system, the volume of that gas will increase

• temperature and pressure are held constant

n ∝ V V1/n1 = V2/n2

Ideal Gases + model for the behaviour of gases

I) The volume of gas particles themselves are negligable compared to the volume of the gas II) There are no attractive forces between the gas particles

Ideal Gas Law formula

PV = nRT

R

Ideal gas constant (in units J/k * mol) Volume in Ideal Gas Law formula must be in m^3, pressure in Pa, and temperature in K

Thermodynamics

The study of how heat works energy + temperature relate to each other

1st Law of Thermodynamics - Conservation of Energy

• energy cannot be created or destroyed

• you can only transfer energy

Heat

A form of energy Thermal energy

Kinetic Energy

the energy of motion Kinetic Energy - 1/2m(^2)

m

mass

V

velocity

Temperature (energetics)

a measure of the average kinetic energy

• energy is added to substance -> internal energy goes up -> particles have more kinetic energy -> particles move faster -> higher temperature

Boltzmann Distribution

Potential Energy

energy that is stored in a system

Enthalpy (H)

total internal energy of a system

• stored in the bonds

ΔH (delta H)

change in Enthalpy

ΔH = Hproducts - Hreactants

Endothermic

• total internal energy goes up (increases)

• absorbs heat

• ΔH is positive

Exothermic

• total internal energy does down (decreases)

• releases heat

• ΔH is negative

Endothermic reaction

Exothermic reaction

Measuring Enthalpy - Heat Capacity calorimetry

the science or act of measuring changes in state variables of a body for the purpose of deriving the heat transfer associated with changes of its state due, for example, to chemical reactions, physical changes, or phase transitions under specified constraints (google)

Calorimetry equation

q = CpmΔT

q

Heat energy (J - energy measured in joules)

Cp

Heat capacity (J/g*K)

ΔT

Change in temperature (K, C)

ΔH

change in enthalpy

Average Bond Enthalpy

The energy needed to break 1 mole of a bond of a gaseous molecule averaged over similar compounds

Stability in reactions

The products are more stable than the reactants, as they have a lower energy level, making it easier to maintain

Hess’s Law

The enthalpy change for a reaction that is carried out in a series of steps is equal to the sum of the enthalpy changes for the individual steps