Rates of Reaction and Energy Changes

• What is the Rate of Reaction a measure of?

  How fast the reaction happens
• What can you measure to follow reaction rates involving gases?

  Change in mass or volume of gas
• How can you measure the rate of a reaction that produces a gas?

  By measuring the mass lost on a balance
• What indicates that a reaction has finished when measuring mass?

  The reading on the balance stops changing
• What can you plot using the results from measuring change in mass?

  A graph of change in mass against time
• What is one method to measure the volume of gas given off in a reaction?

  Using a gas syringe
• When can you tell that a reaction has finished when measuring gas volume?

  When no more gas is produced
• What happens to the rate of reaction when the surface area of a solid increases?

  The rate of reaction increases
• How does changing the concentration of acid affect the rate of reaction?

  Higher concentration leads to a faster reaction
• What is the effect of temperature on reaction rates?

  Higher temperatures increase the reaction rate
• What is the visual indicator of a reaction between sodium thiosulfate and hydrochloric acid?

  Formation of a yellow precipitate of sulfur
• How can you measure the effect of temperature on reaction rate?

  By timing how long it takes for a mark to disappear
• What does a shorter time taken for a mark to disappear indicate?

  A faster rate of reaction
• What does a steeper gradient on a rate of reaction graph indicate?

  A faster rate of reaction
• What is the equation for calculating the gradient of a graph?

  Gradient = change in y / change in x
• How do you calculate the rate of reaction from a graph?

  By finding the gradient of the graph
• What does a tangent on a curve represent in terms of reaction rate?

  The gradient at a specific point on the curve
• What is collision theory?

  The theory explaining reaction rates based on collisions
• What is activation energy?

  The minimum energy needed for a reaction to start
• How does increasing temperature affect particle collisions?

  It increases the frequency and energy of collisions
• How does increasing concentration affect reaction rates?

  It increases the likelihood of collisions
• What happens when solid reactants are broken into smaller pieces?

  The rate of reaction increases due to more surface area
• What is a catalyst?

  A substance that increases reaction rate without changing
• How do catalysts affect activation energy?

  They lower the activation energy needed for reactions
• What role do enzymes play in biological reactions?

  They catalyze chemical reactions in living cells
• What is an exothermic reaction?

  A reaction that gives out energy to surroundings
• What is an endothermic reaction?

  A reaction that takes in energy from surroundings
• What does the activation energy represent on a reaction profile?

  The energy needed to start a reaction
• What happens if the energy input is less than the activation energy?

  No reaction will occur
• What do reaction profiles show in a reaction?

  Energy levels of reactants and products
• How can you determine if a reaction is exothermic or endothermic using reaction profiles?

  By observing energy release or absorption
• In an exothermic reaction, where are the products in relation to the reactants?

  At a lower energy level than reactants
• What does the difference in height on a reaction profile represent in an exothermic reaction?

  The energy given out in the reaction
• What characterizes an endothermic reaction in terms of energy levels?

  Products are at a higher energy than reactants
• What does the height difference in an endothermic reaction profile indicate?

  The energy taken in during the reaction
• What is activation energy?

  The minimum energy needed to start a reaction
• How is activation energy represented on a reaction profile?

  As the energy difference to the highest point
• What analogy is used to explain activation energy?

  Climbing a hill before skiing down
• What happens if the energy input is less than the activation energy?

  No reaction will occur
• What is the procedure to measure temperature changes in a reaction?

  1. Use a polystyrene cup in a beaker.
  2. Add a known volume of the first reagent.
  3. Measure the initial temperature.
  4. Add a measured mass/volume of the second reagent.
  5. Stir and cover the cup.
  6. Record the maximum or minimum temperature.
  7. Calculate the temperature change.