AQA GCSE Chemistry Topic 6: The Rate and Extent of Chemical Change

Rate of Reaction

• Definition: Rate of reaction can be expressed by:
  • Rate of reaction = amount of reactant used / time
  • Rate of reaction = amount of product formed / time
• Measurement:
  • Quantity can be measured by mass (grams) or volume (cm³).
  • Units of rate: g/s, cm³/s, or mol/s (using moles instead of mass or volume).

Graphical Analysis

• Rates can be determined graphically by:
  • Drawing tangents to curves and using the slope of the tangent.
  • Calculating the gradient of a tangent on the graph to measure rate at a specific time.

Factors Affecting Reaction Rates

• Factors:
  • Concentration
  • Pressure
  • Surface area
  • Temperature
  • Catalysts

Collision Theory and Activation Energy

• Collision Theory:
  • Reactions occur when particles collide with sufficient energy.
• Activation Energy:
  • Minimum energy required for particles to react.
• Increasing Factors:
  • Higher concentration, pressure, and surface area increase collision frequency, thus increasing reaction rate.
  • Higher temperature increases collision frequency and energy, accelerating reaction rate.

Catalysts

• Function: Speed up reactions without being consumed.
• Biological Catalysts: Enzymes act as catalysts in biological systems.
• Characteristics:
  • Not part of the chemical equation.
  • Decrease activation energy, increasing the proportion of particles with sufficient energy to react.
  • Provide an alternative reaction pathway with lower activation energy.

Note: Content in bold is specifically for Higher Tier studies.

Source: Physics and Maths Tutor