GCSE Chemistry A (Triple) OCR

States of Matter

States of Matter

Particles

• There are three common states of matter - solid, liquid, and gas.
• The particles are arranged and move differently in these three states.
• Solids have a fixed shape and volume. In a solid, particles vibrate around fixed positions and are close together.
• Liquids fill the bottom of a container, and they can be poured. In a liquid, particles can move around each other and are close together.
• Gases completely fill their containers. In a gas, particles move freely and are far apart from each other.

Changes of State

• Melting and Freezing: The change from solid to liquid is melting, and from liquid to solid is freezing. During these changes of state, the temperature remains constant.
• Boiling and Condensing: The transition from liquid to gas is boiling or evaporation, and from gas to liquid is condensation. During these changes, the temperature remains constant.
• Sublimation and Deposition: Some substances can change directly from solid to gas (sublimation) and from gas to solid (deposition) without becoming a liquid.

Understanding Kinetic Theory

• The kinetic theory helps to explain the different properties of solids, liquids, and gases.
• All particles are in constant motion. The energy of this motion is called kinetic energy.
• Higher temperatures translate to more kinetic energy, meaning that particles move faster.

Energy Needed for Changes of State

• The energy needed to change a substance from one state to another is known as the Latent Heat.
• Specific latent heat is the energy required to change 1 kg of a substance from one state to another without changing its temperature.
• The specific latent heat of fusion refers to the change from solid to liquid (or vice versa).
• The specific latent heat of vaporisation refers to the change from liquid to gas (or vice versa).

Internal Energy

• The energy stored by particles within a system is called internal energy.
• An increase in internal energy can result from an increase in heating (leading to higher kinetic energy) or by doing work on the system (leading to an increase of potential energy).

Properties of Gases

• Random motion and collisions of molecules causes pressure.
• Increasing the temperature of a gas will increase the speed and kinetic energy of the molecules, thus increasing pressure.
• The relationship between pressure, volume and temperature is outlined by the equation of state PV=nRT, where P is pressure, V is volume, n is the number of moles, R is the gas constant and T is temperature.