3.5 - Reaction rates and equilibrium (qualitative) Flashcards
Define ‘rate of reaction’ ?
Rate of reaction : The change in the concentration of reactants or products in a given time period
What is the equation for the rate of reaction ?
Rate = Change in concentration / time
Do you know how to calculate the rate of reaction from a graph ?
Yes
Do you know how to calculate the rate of reaction using a tangent ?
Yes
What are the factors effecting rate of a reaction ?
- Concentration ( or pressure when reactants are gases )
- Temperature
- Catalyst
- Surface area ( of solid reactants )
Explain the effect of concentration on the rate of reaction ?
- As the concentration of the reactants increases, the rate of the reaction increases
- As the concentration increases, the number of particles per unit volume increases
- This means particles are closer together and collide more and therefore collide successfully more frequently per time period
- This increases the rate of the reaction
Explain the effect of pressure on the rate of reaction ?
- As the pressure increases, the rate of the reaction increases
- This increases the number of gas molecules per unit volume
- This means gas molecules are closer together and collide as well as collide successfully more frequently per time period
- This causes the rate of the reaction to increase
Explain the effect of temperature on the rate of reaction ?
- As the temperature increases, the rate of the reaction increases
- This causes the kinetic energy of molecules to increase causing them to vibrate and move more rapidly
- This causes them to collide and collide successfully more frequently per time period leading to na increase in the rate of the reaction
Explain the effect of surface area on the rate of reaction ?
- As the surface area of reactants increases, the rate of the reaction increases
- This means there are more molecules available to be reacted with resulting in more collisions and more successful collisions per time period
- This results in an increase in the rate of the reaction
How can you measure the rate of a reaction ?
- By measuring the removal of reactants/ decrease in concentration of reactants ( by using a balance )
- By measuring the formation of products/ increase in concentration ( Collecting volume of gas produced using a glass syringe )
Define ‘catalyst’ ?
Catalyst : A substance that changes the e rate of a chemical reaction by lowering the activation energy and providing an alternative reaction pathway without being used up itself
What are the two types of catalysts ?
- Homogenous catalyst
- Heterogenous catalyst
Define ‘Homogenous catalyst’’ ?
Homogenous catalyst : A catalyst that has the same physical state as the reactants
Define ‘Heterogenous catalyst’ ?
Heterogenous catalyst : A catalyst that has a different physical state from the reactants
Explain why catalysts are important for the economy and sustainability ?
- Catalysts increase the rate of the reaction by lowering the activation energy and providing an alternative reaction pathway without being
- This reduced the temperature required and therefore lowers energy demands which is less costly
- Lower energy demands means less electricity/ fossil fuels are used which in turn reduces carbon dioxide emissions
Draw a diagram representing the Boltzmann distribution?
What does the origin of the Boltzmann distribution mean ?
The origin means there are no molecules that have no energy ( all molecules have energy )
Draw a diagram of the Boltzmann distribution showing the effect of a catalyst ?
Explain the effect of a catalyst on the Boltzmann distribution and rate of reaction ?
- A catalyst increases the rate of the reaction by lowering the activation energy required and providing and alternative reaction pathway
- This means a greater number of molecules have more molecular energy than the activation energy
Draw a diagram of the Boltzmann distribution showing the effect of temperature ?
Explain the effect of temperature on the Boltzmann distribution and the rate of the reaction ?
- If the temperature is increased, the number of molecules with molecular energy above the activation energy required increases
- This causes the Boltzmann distribution to shift to the right and have a smaller curve ( as number of molecules remains the same )
What are the conditions for a dynamic equilibrium?
- A closed system
- The concentration or reactants and products remains constant
- The rate of the forward reaction equals the rate of the backward reaction
State le Chantelier’s principle ?
The position of a dynamic equilibrium shifts to minimise the effect of the change
What factors affect a dynamic equilibrium ?
- Temperature
- Pressure
- Concentration
Explain the effect of temperature on a dynamic equilibrium ?
- As the temperature increases, the equilibrium moves to the right/ left in the endothermic direction
- As the temperature decreases, the equilibrium moves to the right/ left in the exothermic direction
- The yield increases/ decreases
Explain the effect of pressure on a dynamic equilibrium ?
- As the pressure increases, the equilibrium moves to the right/ left where there are the least moles
- As the pressure decreases, the equilibrium moves to the right/ left where there are the most moles
- The yield increases/ decreases
Explain the effect of concentration on a dynamic equilibrium ?
Explain why compromise conditions for an equilibrium reaction may be required ?
- A low temperature results in a low rate
- A higher temperature is required to increase the rate/ frequency of collisions
- A high pressure poses a safety risk and requires a lot of energy to maintain so it very costly
What is the symbol showing a dynamic equilibrium ?
—->
<—-
Draw a diagram showing how the concentration of reactants / products changes during dynamic equilibrium?
What is the expression for the equilibrium constant ? ( Kvc )
Kvc = [ products ] / [ reactants ]
Do you know how to write an expression for the equilibrium constant ?
Yes
Do you know how to calculate the equilibrium constant and its units ?
Yes
Can you estimate the position of the equilibrium from its equilibrium constant ?
Yes
What does the value of the equilibrium constant represent ?
The magnitude of K, indicates the relative proportions of reactants and products in the equilibrium system
How does the equilibrium constant show us the relative position of the equilibrium ?
- a K, value of 1 indicates a position of equilibrium that is halfway between reactants and products
- a K, value > 1 indicates a position of equilibrium that is towards the products
- a K, value < 1 indicates a position of equilibrium that is towards the reactants
