C8 - Rates and Equilibrium

• How can you find out the rate of a chemical reaction?

  By monitoring reactants used or products made
• What does the gradient of a line on a reaction graph indicate?

  The rate of reaction at that time
• How do you calculate the rate of reaction at a specific time?

  Draw the tangent and calculate its gradient
• What is the equation for calculating the mean rate of reaction?

  Mean rate = quantity of reactant used / time
• Why might no more gas be given off in a reaction with marble chips?

  All reactants have been used up
• What happens to the mass of a reaction mixture when a gas is produced?

  The mass decreases as gas escapes
• What is activation energy?

  The minimum energy needed for a reaction
• How does increasing surface area affect reaction rate?

  It increases collision frequency between particles
• What effect does increasing temperature have on reaction rate?

  It increases the rate due to more energetic collisions
• Why does raising temperature increase reaction rate according to collision theory?

  Particles collide more often and with more energy
• What happens to the rate of reaction when temperature is increased by 10 °C?

  The rate roughly doubles
• How does increasing concentration affect reaction rate?

  It increases the frequency of collisions
• What is the effect of increasing pressure on reacting gases?

  It increases the frequency of collisions
• What is a catalyst?

  A substance that speeds up a reaction
• How do catalysts affect chemical reactions?

  They speed up reactions without being used up
• What happens to catalysts in chemical plants over time?

  They can become poisoned and stop working
• How are reversible reactions represented?

  Using the ⇌ sign
• What occurs in a reversible reaction?

  Products can react to form original reactants
• What is the relationship between exothermic and endothermic reactions in reversible processes?

  Energy transferred is equal in both directions
• How does energy transfer work in reversible reactions?

  Energy is conserved and transferred equally
• What happens to energy in a reversible reaction?

  Energy is transferred equally in both directions
• What type of reaction is it when A and B form C and D and releases energy?

  Exothermic reaction
• What type of reaction occurs when C and D react to form A and B?

  Endothermic reaction
• What is the formula for hydrated copper(II) sulfate?

  CuSO₄.5H₂O
• What happens when blue copper(II) sulfate is heated?

  It becomes white anhydrous copper(II) sulfate
• What are the key points about reversible reactions?

  • One reaction is exothermic, the other is endothermic.
  • Energy transferred in one direction equals energy transferred back.
• What occurs in a closed system during a reversible reaction?

  The rate of forward and reverse reactions is equal
• What happens as the concentration of products builds up in a reversible reaction?

  • Rate of products forming increases.
  • Rate of reactants forming decreases.
  • Eventually, both rates equalize at equilibrium.
• What is dynamic equilibrium in a reversible reaction?

  Continuous forward and reverse reactions at equal rates
• How does changing the concentration of a reactant affect equilibrium?

  It shifts the equilibrium position to favor products
• What is Le Chatelier's Principle?

  Equilibrium shifts to counteract changes in conditions
• What happens when the concentration of chlorine gas is lowered in a reversible reaction?

  The rate of the forward reaction decreases
• What factors can change the composition of an equilibrium mixture?

  • Changes in concentration
  • Changes in pressure
  • Changes in temperature
• How does increasing pressure affect a reversible reaction producing more gas molecules?

  It decreases the amount of products formed
• How does increasing pressure affect a reversible reaction producing fewer gas molecules?

  It increases the amount of products formed
• What happens to the equilibrium position when pressure is increased in the reaction 2NO₂(g) ⇌ N₂O₄(g)?

  It shifts to the right, favoring N₂O₄
• What effect does changing temperature have on a closed system at equilibrium?

  It changes the relative amounts of reactants and products
• What happens to the equilibrium when the temperature is increased in an endothermic reaction?

  It favors the endothermic reaction
• What are the effects of temperature changes on equilibrium in reversible reactions?

  • Increasing temperature favors endothermic reactions.
  • Decreasing temperature favors exothermic reactions.