Kinetics and equilibrium flashcards

Kinetics explores how quickly chemical reactions occur and what factors influence reaction rate. Students must understand how concentration, temperature, surface area, and catalysts affect rate, and be able to explain these using collision theory and Maxwell-Boltzmann energy distributions. The activation energy concept is central, as is the role of a catalyst in providing an alternative pathway of lower activation energy. Equilibrium describes the dynamic state reached in a reversible reaction when forward and reverse rates are equal. Students must apply Le Chatelier's principle to predict how changes in concentration, pressure, and temperature shift equilibrium position, and use the equilibrium constant expression Kc to quantify the position of equilibrium. Understanding that temperature changes alter the value of Kc, while other changes do not, is a key distinction that students frequently overlook.

1. Card 1

   What is the definition of reaction rate?

   Reaction rate is the change in concentration of a reactant or product per unit time, typically expressed in mol dm-3 s-1.

2. Card 2

   State the basic requirements for a successful collision between reactant particles.

   Particles must collide with the correct orientation and with energy equal to or greater than the activation energy.

3. Card 3

   How does increasing temperature affect reaction rate, and why?

   Rate increases because particles have greater kinetic energy, so more collisions exceed the activation energy and the collision frequency also rises.

4. Card 4

   What does a Maxwell-Boltzmann distribution show?

   It shows the distribution of kinetic energies among particles in a gas or solution; the area beyond the activation energy represents particles able to react.

5. Card 5

   How does a catalyst increase reaction rate?

   A catalyst provides an alternative reaction pathway with a lower activation energy, so a greater proportion of collisions are successful.

6. Card 6

   What is dynamic equilibrium?

   Dynamic equilibrium exists when the forward and reverse reaction rates are equal, so macroscopic concentrations remain constant while both reactions continue.

7. Card 7

   Write the Kc expression for: aA + bB ⇌ cC + dD

   Kc = [C]^c [D]^d / [A]^a [B]^b. Kc uses equilibrium molar concentrations; pure solids and liquids are omitted from the expression.

8. Card 8

   What does a large value of Kc indicate about equilibrium position?

   A large Kc means the equilibrium lies to the right, so products are favoured and their concentrations are much greater than those of reactants.

9. Card 9

   State Le Chatelier's principle.

   Le Chatelier's principle states that if a system at equilibrium is disturbed, it shifts to oppose the change and restore a new equilibrium position.

10. Card 10

    How does increasing pressure affect a gaseous equilibrium?

    The equilibrium shifts towards the side with fewer moles of gas, reducing pressure. If both sides have equal moles of gas, there is no shift.

11. Card 11

    How does temperature change affect the value of Kc?

    Temperature is the only common factor that changes the value of Kc. Increasing temperature favours the endothermic direction, altering the constant itself.

12. Card 12

    Why does a catalyst not change the equilibrium position or Kc?

    A catalyst speeds up both forward and reverse reactions equally, so equilibrium is reached faster but the equilibrium position and Kc remain unchanged.

• Students often confuse reaction rate with equilibrium position, incorrectly stating that a catalyst shifts the equilibrium towards products rather than simply helping equilibrium be reached more quickly.
• A very common error is claiming that increasing concentration or pressure changes the value of Kc, when in fact only a change in temperature alters Kc.
• When applying Le Chatelier's principle to pressure changes, students frequently forget to check whether the total moles of gas are equal on both sides, leading to incorrect predictions of no shift when a shift does occur, or vice versa.

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