Physical Chemistry

• What type of reaction releases energy to the surroundings?

  Exothermic reactions
• What happens to the temperature of surroundings during exothermic reactions?

  Temperature increases
• What is an example of an exothermic reaction?

  Combustion
• What is the general equation for an exothermic reaction involving methane?

  CH4 + 2O2 → CO2 + 2H2O + Energy
• What type of reaction absorbs energy from the surroundings?

  Endothermic reactions
• What happens to the temperature of surroundings during endothermic reactions?

  Temperature decreases
• What is an example of an endothermic reaction?

  Photosynthesis
• What is the general equation for an endothermic reaction involving calcium carbonate?

  CaCO3 + Energy → CaO + CO2
• What does ΔH represent in chemical reactions?

  Difference in energy between reactants and products
• What does a negative ΔH indicate about a reaction?

  It is an exothermic reaction
• What does a positive ΔH indicate about a reaction?

  It is an endothermic reaction
• In what units is ΔH measured?

  kJ/mol
• What do energy profile diagrams illustrate for exothermic and endothermic reactions?

  • Exothermic: Products have lower energy than reactants.
  • Endothermic: Products have higher energy than reactants.
• What is bond energy?

  Energy required to break a bond
• How do you calculate ΔH using bond energies?

  ΔH = Total Energy to Break Bonds - Total Energy to Form Bonds
• What is the ΔH for the reaction H2 + Cl2 → 2HCl with given bond energies?

  −184 kJ/mol
• What is the formula for the rate of reaction?

  Rate of Reaction = Change in Quantity / Time Taken
• In what units can the rate of reaction be measured?

  mol/s, cm³/s, g/s
• What factors affect the rate of reaction?

  1. Temperature: Increases kinetic energy.
  2. Concentration/Pressure: More particles in volume.
  3. Surface Area: Smaller particles increase collisions.
  4. Catalysts: Lower activation energy.
• How does temperature affect the rate of reaction?

  Increases kinetic energy and collision frequency
• How does concentration affect the rate of reaction?

  Higher concentration increases collision frequency
• How does surface area affect the rate of reaction?

  Smaller particles create more collisions
• What role do catalysts play in reactions?

  Lower activation energy for faster reactions
• What do catalysts provide in a reaction?

  An alternative reaction pathway
• What is an example of a catalyst in a reaction?

  Manganese dioxide in hydrogen peroxide decomposition
• What methods can be used to measure the rate of reaction?

  1. Measuring gas production.
  2. Observing mass loss.
  3. Color change/precipitate formation.
• How can you measure gas production in a reaction?

  Use a gas syringe or inverted measuring cylinder
• How can you observe mass loss in a reaction?

  Measure mass as gas escapes
• How can you measure color change in a reaction?

  Use a colorimeter or observe a cross
• What is the reaction of hydrochloric acid with calcium carbonate?

  CaCO3 + 2HCl → CaCl2 + H2O + CO2
• How can you measure CO2 volume in the reaction with hydrochloric acid?

  Measure with a gas syringe
• What is the reaction between sodium thiosulfate and hydrochloric acid?

  Na2S2O3 + 2HCl → 2NaCl + H2O + SO2 + S
• How can you measure the time for sulfur precipitate to obscure a cross?

  Observe the time for a cross to disappear
• What are the characteristics of reversible reactions?

  • Can go in both directions.
  • Dynamic equilibrium: Forward and reverse reactions occur at the same rate.
  • Concentrations of reactants and products remain constant.
• What is an example of a reversible reaction?

  Haber process: N2 + 3H2 ↔ 2NH3
• What conditions affect equilibrium in reversible reactions?

  1. Temperature: Higher temperature favors endothermic reaction.
  2. Pressure: Higher pressure favors fewer gas molecules.
  3. Concentration: Increasing reactant concentration shifts equilibrium toward products.