Matter in Our Surroundings

The One Thing

Matter consists of continuously moving particles with spaces between them and mutual attraction. The arrangement, motion, and energy of these particles determine whether matter is solid, liquid, or gas, while changes in temperature or pressure can produce changes of state.

Reactions, Processes and Experiments

Key Terms

• Matter: Anything that has mass and occupies space.
• Particle of matter: A very small unit that makes up matter; particles may be atoms, molecules, or ions.
• Diffusion: The mixing of particles of two or more substances due to their continuous motion.
• Solid: A state of matter with a fixed shape and fixed volume because its particles are closely packed and strongly attracted.
• Liquid: A state of matter with a fixed volume but no fixed shape; it takes the shape of its container.
• Gas: A state of matter with neither fixed shape nor fixed volume; its particles are far apart and move freely.
• Melting: The change of a solid into a liquid on heating.
• Melting point: The temperature at which a solid changes into a liquid at atmospheric pressure; ice melts at 273.15 K or 0°C.
• Freezing: The change of a liquid into a solid on cooling.
• Boiling: The rapid change of a liquid into a gas throughout the liquid at a fixed temperature.
• Boiling point: The temperature at which a liquid changes into a gas throughout its volume at atmospheric pressure; water boils at 373.15 K or 100°C.
• Evaporation: The slow conversion of a liquid into vapour from its surface at temperatures below its boiling point.
• Condensation: The change of a gas or vapour into a liquid on cooling.
• Sublimation: The direct change of a solid into a gas without passing through the liquid state, or the reverse process.
• Latent heat: The heat energy absorbed or released during a change of state without a change in temperature.
• Latent heat of fusion: The heat required to convert 1 kilogram of a solid into liquid at its melting point without changing temperature.
• Latent heat of vaporisation: The heat required to convert 1 kilogram of a liquid into gas at its boiling point without changing temperature.
• Kelvin scale: The SI temperature scale; temperature in kelvin is related to Celsius by K = °C + 273.15.
• Pressure: Force acting per unit area; changing pressure can bring about changes in the state of matter.
• Kinetic energy of particles: The energy associated with particle motion; it increases when temperature increases.
• Specific latent heat: The latent heat required per unit mass for a change of state; in the formula Q = mL, L is specific latent heat.
• Atmospheric pressure: Pressure exerted by the atmosphere; 1 atmosphere is approximately equal to 1.013 × 10^5 pascals.

Easily Confused

• Boiling and evaporation: Boiling is rapid, occurs throughout a liquid, and takes place at a fixed boiling point; evaporation is slow, occurs only at the surface, and can occur at any temperature.
• Melting and freezing: Melting changes a solid into a liquid on heating; freezing changes a liquid into a solid on cooling.
• Boiling point and melting point: The boiling point is the temperature at which a liquid changes into a gas throughout its volume; the melting point is the temperature at which a solid changes into a liquid.
• Evaporation and condensation: Evaporation changes a liquid into vapour from its surface; condensation changes a gas or vapour into a liquid on cooling.
• Sublimation and ordinary melting followed by boiling: Sublimation changes a solid directly into a gas without passing through the liquid state.
• Latent heat and temperature change: Latent heat changes the state without changing temperature, whereas heating outside a change of state increases temperature.
• Celsius and Kelvin scales: 0°C = 273.15 K and 100°C = 373.15 K; the conversion formula is K = °C + 273.15 or °C = K − 273.15.
• Liquids and gases under pressure: Liquids have limited compressibility, whereas gases are highly compressible because their particles have large spaces between them.

What Gets Asked

• Explain how the arrangement, spacing, motion, and attraction of particles account for the properties of solids, liquids, and gases. The mark-losing error is failing to relate fixed shape, fixed volume, or compressibility to particle arrangement.
• Distinguish boiling from evaporation. The specific errors are stating that evaporation occurs throughout the liquid, or that it occurs only at the boiling point.
• Explain why evaporation causes cooling. The required point is that faster, higher-energy particles escape, leaving particles with lower average energy.
• State factors affecting the rate of evaporation: surface area, temperature, wind speed, and humidity. The rate increases with surface area, temperature, and wind speed, but decreases with humidity.
• Convert temperatures using K = °C + 273.15 and °C = K − 273.15, including 0°C = 273.15 K and 100°C = 373.15 K. The common slip is omitting or misusing 273.15.
• Use the specific latent heat equation Q = mL. The symbols must be identified correctly: Q is heat energy, m is mass, and L is specific latent heat.
• Identify examples of sublimation, including camphor, naphthalene, ammonium chloride, and solid carbon dioxide. The key distinction is direct conversion between solid and gas without the liquid state.