PMT flashcards chapter 10

• What is the equation used to calculate rate?

  Rate = change in concentration / time
• What is the unit for rate of reaction?

  mol dm^-3s^-1
• What must particles do in order to react?

  Collide with sufficient energy and correct orientation
• Do most collisions result in a reaction?

  No
• What are the factors that affect the rate of reaction?

  • Temperature
  • Pressure
  • Concentration
  • Surface area
  • Catalyst
• What is the effect of increasing temperature on the rate of reaction?

  Increased temperature leads to increased rate
• Why does increasing temperature increase the rate of reaction?

  More particles have energy greater than activation energy

  
• What is the effect of increasing concentration/pressure on the rate of reaction?

  Increased concentration/pressure leads to increased rate
• Why does increasing concentration/pressure increase the rate of reaction?

  More particles in a given volume lead to more collisions
• What are the variables that can be monitored to calculate the rate of reaction?

  • Concentration of reactant or product
  • Gas volume of products
  • Mass of substances formed
• How to calculate rate from a concentration-time graph?

  Draw a tangent and find the gradient
• What is the equation for the gradient of a tangent?

  Gradient = change in y / change in x
• What is a catalyst?

  A substance that increases the rate of reaction

  
• How do catalysts work to increase the rate of reaction?

  They provide an alternate pathway with lower activation energy

  
• What does homogeneous catalyst mean?

  A catalyst in the same phase as reactants
• What does heterogeneous catalyst mean?

  A catalyst in a different phase from reactants
• What are catalytic converters?

  Devices in vehicles to reduce toxic emissions
• Define activation energy.

  The minimum energy for a reaction to occur
• What are some important features of Boltzmann distribution?

  • Area under the curve = total number of molecules
  • Area under the curve does not change with conditions
  • Curve starts at the origin
  • Curve does not touch or cross the energy axis
  • Only molecules with energy > activation energy can react
• What are the axes in a Boltzmann distribution?

  X axis - energy, Y axis - number of molecules

  
• How does increasing temperature affect the Boltzmann distribution curve?

  • Shifts the curve to the right
  • Increases the area under the curve
  • More molecules exceed activation energy
• How does a catalyst affect the Boltzmann distribution curve?

  • Lowers the activation energy
  • Increases the number of molecules exceeding activation energy
  • Shifts the curve to the right
• What does dynamic equilibrium mean?

  Rates of forward and reverse reactions equal
• What occurs in a closed system at dynamic equilibrium?

  Concentrations of reactants and products remain constant
• What factors can alter the position of equilibrium?

  • Concentration of reactants or products
  • Pressure
  • Temperature
• What is Le Chatelier’s principle?

  Equilibrium shifts to reduce disturbance
• In the reaction CH4(g) + H2O(g) ⇌ CO(g) + 3H2(g), what happens if temperature increases?

  Equilibrium position shifts to the right
• Why does the equilibrium position shift to the right when temperature increases in an endothermic reaction?

  Forward reaction absorbs heat, increasing yield
• In the reaction CH4(g) + H2O(g) ⇌ CO(g) + 3H2(g), what happens if pressure increases?

  Equilibrium position shifts to the left
• Why does increasing pressure shift the equilibrium to the left in the reaction CH4(g) + H2O(g) ⇌ CO(g) + 3H2(g)?

  Forward reaction produces more moles of gas
• Why might an industrial chemist use high pressure for hydrogen production in the reaction CH4(g) + H2O(g) ⇌ CO(g) + 3H2(g)?

  Increases collision frequency, speeding up reaction
• What effect does a catalyst have on the position of equilibrium?

  No effect on equilibrium position
• What conditions affect the value of Kc?

  • Concentration
  • Catalyst
  • Pressure
  • Temperature
• For the reaction 2[A] + 3[B] + [C] ⇌ [D] + 4[E], what is the expression for Kc?

  Kc = \frac{[D][E]^4}{[A]^2[B]^3[C]}

  
• What are the units for Kc?

  mol^-1 dm^-3
• For what type of system is Kc relevant?

  Homogeneous systems in equilibrium
• What does Kc being greater than 1 suggest for the position of equilibrium?

  Equilibrium shifts to the right

  
• What does Kc being less than 1 suggest for the position of equilibrium?

  Equilibrium shifts to the left

  
• What effect does decreasing the temperature of an endothermic reaction have on Kc?

  Kc decreases
• What effect does increasing the temperature of an endothermic reaction have on Kc?

  Kc increases