Gas laws : MCQ 3

States of Matter

• There are three states of matter: solids, liquids, and gases.
• Solids have a fixed shape and volume due to tightly packed particles that vibrate when heated.
• When heated to the melting point, particles break free, resulting in an increase in volume as the solid becomes a liquid.
• Liquids have a fixed volume at a given temperature, and particles are close together but can slide over each other.
• At boiling point, particles break completely free, resulting in a large increase in volume.
• Gases have no fixed shape or volume, and particles move randomly in all directions.

Diffusion

• Diffusion is the spontaneous spreading out of a substance due to the natural movement of its particles.
• Diffusion occurs in gases and liquids.
• Examples of diffusion include:
  • HCl and NH₃ diffusing to form Ammonium chloride.
  • Potassium permanganate crystals in water.

Gas Laws

• The gas laws explain the change in volume of a gas when different pressures and temperatures are exerted on the gas.
• Temperature is measured in Kelvin (K), with 0°C equal to 273K.
• Pressure is measured in Pascals (Pa).
• Volume is measured in cm³.
• Standard Temperature and Pressure (s.t.p) conditions are:
  • Standard temperature: 273K
  • Standard pressure: 101,325 Pa
  • Molar volume at s.t.p: 1 mole = 22.4L = 22,400cm³

Boyle's Law

• Boyle's Law states that, at constant temperature, the volume of a fixed mass of any gas is inversely proportional to the pressure of the gas.
• When pressure is increased, the volume of the gas decreases.
• Volume is inversely proportional to pressure: 1/Pressure

Charles' Law

• Charles' Law states that, at constant pressure, the volume of a given mass of any gas is directly proportional to the Kelvin temperature.
• When temperature is increased, the volume of the gas increases proportionally.

Combined Gas Law

• The combined gas law is a combination of Boyle's Law and Charles' Law.
• The law states that the volume of a gas is inversely proportional to the pressure and directly proportional to the temperature.
• Example: finding the volume of a gas at s.t.p.

Gay-Lussac's Law of Combining Volumes

• Gay-Lussac's Law states that the volumes of gases reacting and the volume of the gaseous products are in simple whole number ratios to each other.
• Example: the reaction of hydrogen and chlorine to form hydrogen chloride.

Avogadro's Law

• Avogadro's Law states that equal volumes of gases, under the same conditions of temperature and pressure, contain equal numbers of molecules.
• 22.4L = 1 mole = 6 × 10²³ molecules at s.t.p.
• Avogadro's Law can be used to write chemical equations, such as the reaction of hydrogen and chlorine to form hydrogen chloride.