Chem- Rates of Reaction

• What do particles need to react ?

  • Collide successfully

  • With sufficient energy

  • Be in correct orientation
• What do particles need to successfully collide ?

  • Particles must have enough energy AND be in the right position
• How does temperature affect the number of collisions and rate of reaction? 


  • Increasing the temperature of a reaction increases the kinetic energy of the particles , frequency of successful collisions also increase,particles collide more often
• A successful collision is when particles have more energy than the required activation energy
• Explain why the rate of reaction increases when temperature increases , in terms of activation energy and collisions between particles ?

  • increasing the temperature means that the particles have more kinetic energy ,so particles move faster,which means that they collide more frequently ,so more particles have greater energy than activation energy. ( if temp. Decreases then it’s the opposite ANS)
• Rate of reaction is all about speed and is defined as the change in concentration of reactants or products per unit time
• Rate of reaction can be calculated using the equation: change in concentration or volume or mass divided by time
• In an experiment with marble chips reacting with hydrochloric acid, carbon dioxide gas is released as the marble chips (calcium carbonate) react with the acid
• The mass lost during the reaction indicates how much carbon dioxide is being given off
• The volume of carbon dioxide released can be plotted against time to observe the reaction progress
• The slope of the graph indicates the rate of reaction - steeper slope means a faster reaction
• The rate of any chemical reaction is fastest at the start and slows down as the reaction progresses
• Successful collisions between reacting particles require enough energy, known as activation energy, to break bonds and start the reaction
• Activation energy is the minimum energy required for a reaction to occur
• Increasing the surface area of a solid (particle size) increases the rate of reaction by allowing more surface for reactions to take place
• Increasing the concentration of a solution or the pressure of a gas increases the rate of reaction by increasing the number of particles in a specific volume, leading to more collisions
• Raising the temperature increases the energy of reactant particles, causing more frequent collisions and a faster rate of reaction
• Increasing temperature increases the energy of reactant particles, leading to more frequent and energetic collisions
• Pressure affects gases by increasing the number of gas particles in a specific volume, causing them to be closer together and collide more frequently
• Catalysts are substances that speed up reactions without being consumed
• A catalyst speeds up a chemical reaction by providing an alternative route with a lower activation energy
• Pressure does not affect the rate of reaction for solids or liquids as their particles are already close together
• Enzymes are biological catalysts that allow reactions to occur faster at lower temperatures
• Different reactions require specific catalysts, such as iron for the Haber process and vanadium for the contact process
• Manganese oxide and lead oxides are examples of catalysts used to decompose hydrogen peroxide
• In a reaction between marble chips and dilute hydrochloric acid, the mass of the flask decreases as carbon dioxide gas escapes
• The reaction ends when all the hydrochloric acid has been used up, indicated by the presence of leftover marble chips and no further decrease in mass
• The rate of reaction is fastest at the beginning, as shown by the steepest part of the curve on a graph plotting mass vs. time
• Using smaller marble chips increases the rate of reaction due to the increased surface area, resulting in a steeper curve on the graph
• Decreasing the concentration of hydrochloric acid lowers the rate of reaction by reducing the frequency of successful collisions between reactant particles
• Fewer particles in a specific volume lead to less frequent successful collisions
• Less frequent successful collisions result in a slower rate of reaction