Kinetic Molecular properties of Gases

• Matter and its Interactions is the focus of Quarter 4 studies.

Week 1: Volume, Pressure, and Kinetic Molecular Theory

• This section investigates the relationship between volume and pressure at constant temperature.
• It also looks at volume and temperature at constant pressure of a gas.
• This section discusses explaining these gas property relationships via the kinetic molecular theory.

Objectives

• Learn the properties of gases.
• Prove that gases exhibit mass, volume, temperature and pressure.
• Study practical applications of Boyle's Law.

Gases

• Gases enter the body through inhalation and exhalation.
• Approximately 16 kg of gases enters the lungs every day.
• Jan Baptista Van Helmont, a Flemish scientist and physicist, first used the word "gas" in the 18th century.
• He derived "gas" from the Greek word "chaos," which means "formless mass."
• Gases are a disorganized, formless type of matter.

General Properties of Gases

• Gases lack a definite shape and volume, adopting the volume of their container by occupying all available space.
• Expansibility is the property of gases to expand when heated and contract when cooled.
• Compressibility is the ability to compress when pressure is applied, and they exert pressure.
• Diffusibility is the ability to diffuse or intermingle with other substances due to negligible intermolecular forces.

Measurable Properties of Gases

• Volume is equivalent to the volume of its container and can be measured in liters (L), milliliters (mL), cubic meters (m³), and cubic centimeters (cm³).
• Pressure is the force exerted by gas molecules on the walls of a container and is measured in Pascals (Pa).
• Standard atmosphere pressure is 1.013 x10⁵ N/m² or 1 atm, which decreases with altitude.
• Common pressure units include 1 atm = 1.013 x10⁵ N/m² = 1.013 x10⁵ Pa, 1 atm = 760 torr = 760 mmHg = 76 cm Hg, and 1 atm = 14.696 psi.
• Temperature reflects the average kinetic energy of gas particles, typically measured using a thermometer in Celsius (°C), Fahrenheit (°F), or Kelvin (K).
• Kelvin is used for calculations involving temperature of gas.
• Useful formulas for temperature conversion: °C = (°F - 32) / 1.8, °F = 1.8°C + 32, K = °C + 273.

Gas Standard Conditions

• Standard Temperature and Pressure (STP) is the standard condition for a gas.
• Standard temperature is the melting point of ice, which is 0°C or 273K.
• Standard pressure is the average atmospheric pressure at sea level, equivalent to 1 atm.
• One mole of gas occupies a volume of 22.4 L.

Boyle's Law

• Boyle's Law states that the pressure of a gas is inversely related to its volume when temperature (T) and amount (n) are constant.
• This means that as volume decreases, pressure increases.
• If a gas has two different conditions, the product of volume and pressure remains constant, expressed as P₁V₁ = P₂V₂ (when T and n are constant).

Problem Solving for Boyle's Law

• Set up a table containing all data.
• To identify initial and final states and conditions.
• Solve for the target or unknown value by rearranging the formula.
• Substitute your knowns into the formula.
• Solve for the unknown.
• Example question, what is the new volume of two liters of gas in a container with 760mm Hg of pressure if the pressure is increased to 1,520 mm Hg?
• Initial Pressure: 760 mm Hg and Final Pressure: 1,520 mm Hg.
• Initial Volume: 2.0 L and What is the Final Volume?
• Use the formula, V₂ = (V₁ x P₁) / P₂ which gets you (2.0 L) (760 mm Hg)/ 1,520 mm Hg and final volume is 1 L.

Boyle's Law in Application

• Boyle's Law can be applied understanding the process of breathing.
• When one inhales, the diaphragm muscles contract, causing the thoracic cavity to expand, increasing its volume, resulting in the decrease of pressure.
• During inhalation, the lungs expand, the pressure in the lungs decreases, and air flows towards the lower pressure in the lungs.
• When inhaling, the volume of the lungs increases, in turn decreases the pressure inside compared to the outer atmosphere.
• When exhaling, the volume of the lungs decreases which in turn increases the pressure inside the lungs compared to the outer atmosphere.
• When filling bike tires with air the gas molecules inside the tire gets compressed and packed closer together which increases the pressure of the gas.
• In soda bottles, carbon dioxide is added after the bottle is pressurized.
• When sealed, the gas in confined pushing against the walls of the bottle.
• When the cap is removed, the volume increases and the gas escapes, leading to a pressure decrease.