10 Reaction rates and equilibrium Flashcards
What is meant by rate of a chemical reaction?
It measures how fast a reactant is being used up or how fast a product is being formed.
What makes a collision effective?
- The particles collide with the correct orientation.
- The particles have sufficient energy to overcome the activation energy barrier of the reaction.
How does increasing the concentration affect the rate of reaction?
- An increase in concentration increases the number of particles in the same volume.
- The particles are closer together and collide more frequently.
- In a given period of time there will be more effective collisions and an increased rate of reaction.
How does increasing the pressure of a gas effect the rate of reaction?
- The concentration of the gas molecules increases as the same number of gas molecules occupy a smaller volume.
- The gas molecules are closer together and collide more frequently, leading to more effective collisions in at the same time.
What is a catalyst?
- A catalyst is a substance that increases the rate of a chemical reaction without being used up in the process.
- It provides an alternative reaction pathway of lower activation energy.
What are the two types of catalysts?
- Homogeneous catalyst
- Heterogeneous catalyst
What is a homogeneous catalyst?
- A homogeneous catalyst has the same physical state as the reactants.
- The catalyst reacts with the reactants to form an intermediate.
- The intermediate then breaks down to give the product and regenerates the catalyst.
What is a heterogeneous catalyst?
- A heterogeneous catalyst has a different physical state from the reactants.
- Reactant molecules are adsorbed (weakly bonded) onto the surface of the catalyst, where the reactant takes place.
- After reaction, the product molecules leave the surface of the catalyst by desorption.
What happens during autocatalysis?
The reaction product acts as a catalyst for that reaction.
What are some features of the Boltzmann distribution?
- No molecules have zero energy.
- The area under the curve is equal to the total number of molecules.
- There is no maximum energy for a molecule- the curve does not meet the x axis.
What happens at a higher temperature?
- More molecules have an energy greater than or equal to the activation energy.
- Therefore a greater proportion of collisions will lead to a reaction, increasing the rate of reaction.
- Collisions will also be more frequent as the molecules are moving faster.
What happens when there is a catalyst?
- A catalyst provides an alternative route with a lower activation energy.
- A greater proportion of molecules now have an energy equal to, or greater than the lower activation energy.
- On collision, more molecules will react to form products.
- The result is an increase in rate of reaction.
In an equilibrium system:
- The rate of the forward reaction is equal to the rate of the reverse reaction.
- The concentration of reactants and products do not change.
Equilibrium systems are…
dynamic
For a reaction to remain in equilibrium, the system must be…
closed
What is le Chatelier’s principle?
It states that when a system in equilibrium is subjected to an external change, the system readjusts itself to minimise the effect of that change.
What effect does changing the concentration of reactants or products have?
- If there are more products formed, the position of the equilibrium has shifted to the right.
- If there are more reactants formed, the position of the equilibrium has shifted to the left.
What effect does changing the temperature have?
- An increase in temperature shifts the equilibrium position in the endothermic direction.
- A decrease in temperature shifts the equilibrium position in the exothermic direction.
What colour does the solution of cobalt chloride change when there is an increase in temperature?
Blue
What colour does the solution of cobalt chloride change when there is a decrease in temperature?
Pink
What colour does the solution of potassium dichromate change when you add sulfuric acid?
Orange, as there is an increase in concentration of H+ ions (Shifts right)
What colour does the solution of potassium dichromate change when you add sodium hydroxide?
Yellow, as there is a decrease in concentration of H+ ions (Shifts left)
What happens when you increase the pressure of the system?
The equilibrium position will shift to the side with fewer molecules, reducing the pressure of the system.
What does the Kc value of 1 tell us?
It indicates a position of equilibrium that is halfway between reactants and products.
What does a Kc value of >1 tell us?
Position of equilibrium towards products.
What does a Kc value of <1 tell us?
Position of equilibrium towards reactants.
