Physical Characteristics of Gases - Physical Science

Kinetic Molecular Theory

Explains the behavior of gases based on the motion of their particles.

States that all matter is made up of tiny particles atoms and molecules.

The temperature of a substance is directly related to the average kinetic energy of its particles.

Charles’s Law

If gas is heated by keeping pressure and mass constant, it will expand. 

As temperature increases, volume increases. 

As temperature decreases, volume decreases.

Boyle’s Law

States that the pressure exerted by a gas of a given mass, kept at a constant temperature is inversely proportional to the volume occupied by it. 

The pressure and volume of a gas are inversely proportional to each other as long as the temperature and the quantity of gas are kept constant.

Constant Temperature

Refers to a condition where the temperature of a system remains unchanged during a process.

In an isothermal process, the system exchanges heat with its surroundings to maintain a constant temperature.

At constant temperature, the average kinetic energy of particles remains constant.

Pressure Increase

Pressure increase refers to the rise in pressure within a system, often due to changes in volume or temperature.

Increasing temperature in a closed system can lead to increased pressure, as gas molecules move faster and collide more forcefully with container walls.

Le Chatelier's Principle in equilibrium systems, increasing pressure will shift the equilibrium position towards the side with fewer gas molecules.

Gay-Lussac’s Law

States that the pressure of an ideal gas is directly proportional to the absolute temperature at constant volume. 

This means that as the temperature of a gas increases, its pressure also increases assuming the volume remains constant.

Graham’s Law

States that the rate of effusion or diffusion of a gas is inversely proportional to the square root of the molar mass of the gas. 

Can be understood by comparing two gases A and B at the same temperature, meaning the gases have the same kinetic energy.

Gas Volume

Refers to the amount of space that a gas occupies, measured in liters L or cubic meters m³.

The relationship between pressure, volume, temperature, and the number of moles of a gas is described by the Ideal Gas Law: PV = nRT.

Standard temperature and pressure STP, defined as 0°C (273.15 K) and 1 atm pressure.

Fixed Volume

Refers to a state where the volume of a substance remains constant regardless of changes in pressure or temperature.

Applies to solids and liquids, which do not compress easily.

The behavior of gases at fixed volume can be analyzed using the ideal gas law PV=nRT.

Gas Compression

Refers to the process of reducing the volume of a gas by applying pressure.

The behavior of gases during compression can be described by the Ideal Gas Law PV=nRT.

As volume decreases, the pressure of the gas increases, temperature remains constant Boyle's Law.

Gas Diffusion

The process by which gas molecules spread from an area of higher concentration to an area of lower concentration.

Occurs due to the random motion of gas particles, driven by kinetic energy.

Factors Influencing Diffusion are temperature, pressure, and molecular weight of the gas affect the rate of diffusion.

Rate of Effusion

Refers to the speed at which gas molecules escape through a small hole into a vacuum or another container.

Graham's Law the rate of effusion is inversely proportional to the square root of the molar mass of the gas.

Temperature and pressure can affect the rate of effusion, higher temperatures increase kinetic energy and effusion rates.

Rate of Diffusion

Refers to how quickly particles spread from an area of high concentration to an area of low concentration.

Temperature, concentration gradient, and particle size significantly affect the rate of diffusion.

Higher temperatures increase kinetic energy, leading to faster diffusion rates.

Gas Pressure

The force exerted by gas molecules colliding with the walls of their container.

Typically measured in units such as atmospheres atm, pascals Pa, or millimeters of mercury mmHg.

Influenced by temperature, volume, and the number of gas molecules Avogadro's principle.

Ideal Gas

A theoretical gas composed of many randomly moving point particles that are not subject to interparticle interactions. 

The requirement of zero interaction can often be relaxed if, for example, the interaction is perfectly elastic or regarded as point-like collisions.

Avogadro’s Law

States that equal volumes of all gases, at the same temperature and pressure, have the same number of molecules.

For a given mass of an ideal gas, the volume and amount moles of the gas are directly proportional if the temperature and pressure are constant.

Average Kinetic Energy

Refers to the mean energy of particles in a substance due to their motion.

It is directly proportional to the temperature of the substance, higher temperatures indicate higher average kinetic energy.

Essential for understanding reaction rates and the energy distribution among molecules in a system.

Absolute Zero

The coldest point on the thermodynamic temperature scale, a state at which the enthalpy and entropy of a cooled ideal gas reach their minimum value. 

The fundamental particles of nature have minimum vibrational motion, retaining only quantum mechanical, zero-point energy-induced particle motion. 

The theoretical temperature is determined by extrapolating the ideal gas law.

Elastic Collisions

Interactions where total kinetic energy is conserved before and after the collision.

Molecular Context in chemistry, this often refers to gas molecules colliding without losing energy.

Unlike elastic collisions, inelastic collisions result in a loss of kinetic energy, often converted to other forms of energy.

Gas Density

Is the mass of a gas per unit volume, typically expressed in grams per liter (g/L).

Gas density is influenced by temperature and pressure; higher temperatures decrease density, while higher pressures increase it.

Intermolecular Forces

The forces of attraction or repulsion between neighboring particles atoms, molecules, or ions.

The main types include hydrogen bonding, dipole-dipole interactions, and London dispersion forces.

Hydrogen Bonding is a strong type of dipole-dipole interaction that occurs when hydrogen is bonded to highly electronegative atoms like oxygen, nitrogen, or fluorine.

Limiting Reagent Calculation

N_{2 (g)} + 3 H₂ —> 2 NH_{3 (g)}

49.84 g N₂  +  10.7 g H₂ —> 60.54 g NH₃

1 mol N₂ = 28 g N₂

3 mol H₂ = 6 g H₂

2 mol NH₃ = 34 g NH₃

49.84 g N₂  x (1 mol N₂/28 g N₂) x (2 mol NH₃/1 mol N₂) x (17 g NH₃/ 1 mol NH₃) = 60.52 g NH₃

No limiting reagent.  Mole Ratio is 1 mol N₂ to 3 mol H₂

Stoichiometric Mass Calculations

Fe₂O_{3 (s)} + 3 CO _(g) → 3 CO_{2 9g)} + 2 Fe _(s)

                      ? g CO  →                 558 g Fe

558 g Fe x (1 mol Fe/56 g Fe) x 

( 3 mol CO/2 mol Fe) x ( 28 g CO/1 mol CO) =

                                 420 g CO = 4.20 x 10² g CO

Calculating Molecular Mass

Stoichiometric Calculation

CO _(g) + 2 H_{2 (g)} → CH₃OH _(l) 

          4.0 g H₂  → ? g CH₃OH

4.0 g H₂  x (1 mol H₂ /2 g H₂) x 

  (1 mol CH₃OH/ 2 mol H₂) x 

(32 g CH₃OH/ 1 mol CH₃OH) = 32 g CH₃OH