chem-paper 2 🧪

• What is the first topic in the second chemistry paper for AQA GCC combined science?

  Rate and extent of chemical change
• How is the rate of a chemical reaction defined?

  It is the speed of the reaction
• How can the rate of a reaction be measured?

  By how quickly reactants are used or products made
• What are the two formulae to calculate the rate of a chemical reaction?

  Amount of chemical divided by time
• What units can be used to measure the amount of a chemical?

  Grams, centimeters cubed, or moles
• If a reaction produces 20 cm³ of gas in 2 seconds, what is the rate?

  10 cm³ per second
• What does the gradient of a rate graph represent?

  The rate of the reaction
• What does a straight line gradient on a rate graph indicate?

  The rate is constant
• How do you calculate the rate from a mass increase of 5 grams over 10 seconds?

  0.5 grams per second
• Why is a reaction graph likely to be curved rather than straight?

  Reactions start quickly and slow down
• How do you find the average rate from a curved graph?

  Use the start and end points
• What is a tangent in relation to a curve on a graph?

  A straight line touching the curve at one point
• How do you draw a tangent accurately on a graph?

  Use a transparent ruler or flip the paper
• What happens to the rate of reaction if the tangent is drawn at a steeper point?

  The rate will be higher
• What are the five factors that can change the rate of a reaction?

  Pressure, concentration, surface area, temperature, catalyst
• What does collision theory state?

  Reactions occur when particles collide with energy
• What is activation energy?

  The minimum energy needed for a reaction
• How does increasing pressure affect the rate of reaction?

  It increases collision frequency
• How does increasing concentration affect the rate of reaction?

  More particles lead to more collisions
• What happens to surface area when a solid is cut into smaller pieces?

  Surface area to volume ratio increases
• How does temperature affect particle movement?

  Particles move faster with more energy
• What is the relationship between temperature and activation energy?

  Higher temperature increases particles with activation energy
• What is a catalyst?

  A substance that speeds up reactions without changing
• How do catalysts lower activation energy?

  By providing an alternative reaction pathway
• How does a reaction profile with a catalyst differ from one without?

  It has a lower activation energy peak
• What is the required practical for investigating concentration's effect on reaction rate?

  • Collect gas using a gas syringe or over water
  • Measure gas produced at different concentrations
  • Control variables: same volume of acid, same mass of reactants
• What is the turbidity method for measuring reaction rate?

  • Reaction between hydrochloric acid and sodium thiosulfate
  • Cross on paper disappears as solution becomes cloudy
  • Time taken for cross to disappear indicates reaction rate
• What is the independent variable in the required practical for concentration and rate of reaction?

  The concentration of the acid
• What is the dependent variable in the required practical for concentration and rate of reaction?

  The rate of reaction measured by gas produced
• What is the control variable in the required practical for concentration and rate of reaction?

  Same volume of acid and mass of reactants
• What is turbidity in the context of chemical reactions?

  Cloudiness of a solution
• How is the rate of reaction measured in the turbidity method?

  By timing how long until the cross disappears
• What is turbidity in a chemical reaction?

  Cloudiness of a solution
• What shape is a conical flask used in the turbidity experiment?

  Triangle-shaped
• What happens to the solution during the reaction between hydrochloric acid and sodium thiosulfate?

  It becomes cloudy due to sulfur precipitate
• How can the turbidity experiment be improved?

  By using a light sensor for measurement
• What is a reversible reaction?

  Products can react to form original reactants
• What happens when hydrated copper sulfate is heated?

  It turns into anhydrous copper sulfate and water
• What is chemical equilibrium?

  Forward and reverse reactions occur at the same rate
• How does chemical equilibrium differ from biological equilibrium?

  It involves rates of reactions, not concentrations