Question 1: Define Collision Theory in the context of chemical reactions.

Answer: Collision Theory states that chemical reactions occur when particles collide with sufficient energy and proper orientation to break existing bonds and form new ones.

Question 2: Explain what is meant by 'activation energy' and its significance in collision theory.

Answer: Activation energy is the minimum energy required for particles to collide with enough force and proper orientation to initiate a chemical reaction.

Question 3: Describe how temperature affects the rate of reaction according to Collision Theory.

Answer: Increasing temperature increases particle energy, leading to more frequent and energetic collisions, thereby increasing the reaction rate.

Question 1: The rate constant (k) for a reaction at 25°C is 0.02 dm³ mol⁻¹ s⁻¹. Calculate the rate of reaction when the concentration of reactant A is 0.5 mol/dm³. Use the rate law: Rate = k [A]^2.

Answer: 0.02 * (0.5)^2 = 0.02 * 0.25 = 0.005 dm³ s⁻¹

Question 2: A reaction doubles its rate when the temperature is increased from 25°C to 35°C. If the activation energy is 50 kJ/mol, calculate the ratio of the number of successful collisions at these temperatures using the Arrhenius equation approximation.

Answer: Using the ratio: (e^{(-Ea/RT1)} / e^{(-Ea/RT2)}) = e^{(Ea/R)(1/T1 - 1/T2)} T1=298K, T2=308K, Ea=50,000 J/mol, R=8.314 J/(mol·K) Ratio ≈ e^{(50000/8.314)(1/298 - 1/308)} ≈ e^{(6018)(0.000112)} ≈ e^{0.675} ≈ 1.96

Question 1: Describe an experiment to investigate how concentration affects the rate of a reaction involving sodium thiosulphate and hydrochloric acid.

Answer: Students would vary the concentration of sodium thiosulphate while keeping other variables constant, then measure the time taken for a precipitate to obscure a mark beneath the reaction vessel, indicating reaction rate. Safety precautions include wearing goggles and gloves, and working in a well-ventilated area.

Question 2: Identify three variables that should be controlled in this experiment and explain why.

Answer: Variables to control include temperature (affects collision energy), surface area of reactants (affects collision frequency), and concentration of hydrochloric acid (to isolate the effect of sodium thiosulphate).

Question 1: In an experiment, doubling the concentration of a reactant resulted in the reaction rate increasing by a factor of four. Explain this observation in terms of collision theory.

Answer: According to collision theory, reaction rate is proportional to the square of concentration for this reaction, so doubling concentration increases the number of successful collisions by four times.

Question 2: A reaction's rate is observed to decrease when an inert gas is added to the reaction mixture at constant volume and temperature. Explain why, based on collision theory.

Answer: Adding an inert gas increases the total pressure but decreases the frequency of effective collisions between reactant particles, thus reducing the reaction rate.

Question 1: Explain how increasing the surface area of a solid reactant affects the rate of reaction according to collision theory. Include in your answer the role of particle collisions.

Answer: Increasing the surface area of a solid reactant exposes more particles to the reactant in the other substance, leading to more frequent collisions. This increases the likelihood of particles colliding with sufficient energy and proper orientation, thus increasing the reaction rate.

Question 1: Explain how Collision Theory influences the design of catalytic converters in automobiles.

Answer: Catalytic converters increase the rate of harmful gas reactions by providing a surface that facilitates more effective collisions at lower energies, reducing activation energy and speeding up pollutant breakdown.

Question 2: Discuss how knowledge of collision frequency and energy can be used to optimise industrial chemical reactions for higher yields.

Answer: Industries can increase temperature, pressure, or surface area to enhance collision frequency and energy, thereby increasing reaction rates and yields. Understanding the collision parameters allows for process optimisation to be both efficient and safe.