Reaction rates and equilibrium Flashcards
(41 cards)
What is the definition of rate of reaction ?
the change in concentration of a reactant or product in a given time
What is the equation and units for rate of reaction ?
- change in concentration / time
- moldm^-3s^-1
What is the definition of activation energy ?
the minimum energy required to start a reaction by the breaking of bonds
What 5 factors can alter the rate of reaction ?
- concentration of reactants
- pressure (when reactants are gases)
- temperature
- catalyst
- surface area (when reactants are solids)
When do reactions happen ?
- when reactants collide with the correct orientation and particles have the minimum kinetic energy needed for them to react
What is the effect of increasing the concentration on reactants on the rate of reaction and why ?
- it increases the rate of reaction
- because there are more particles in the same volume and so there are more frequent successful collisions
What is the effect of increasing the pressure on the rate of reaction and why ?
- it increases the rate of reaction
- because there are more particles in the same volume (same particles in a smaller volume) and so there are more frequent successful collisions
What is the effect of increasing the temperature on the rate of reaction and why ?
- it increases the rate of reaction
- because the particles have more kinetic energy, so there are more successful collisions
What is the effect of adding a catalyst on a rate of reaction and why ?
- it increases the rate of reaction
- because the catalyst decreases the activation energy, so more particles have enough energy to react so there are more frequent successful collisions
How can the progress of a reaction be followed in terms of reactants ?
by monitoring the change in concentration of reactants
How can the progress of a reaction be followed in terms of products ?
by monitoring the change of concentration of products
If a reaction produces a gas, what are the two ways of determining the rate of reaction ?
- monitoring volume of gas lost
- monitoring mass lost
How do calculate the initial rate of a reaction ?
- plot a graph of volume of gas (or mass lost) on the y-axis against time on the x-axis
- draw a tangent at t=0
- calculate the gradient of the tangent (change in y / change in x) which is the rate of reaction
What is a catalyst ?
a substance that increases the rate of a reaction without being used up in the process
How does a catalyst increase the rate of a reaction ?
it provides an alternative reaction pathway by lowering the activation energy of the reaction
How does a heterogeneous catalyst work ?
- the reactants are absorbed onto the surface of the catalyst
- the reaction takes place : old bonds weaken and new bonds form
- the products are deabsorbed from the catalyst and diffuse away
What is a heterogeneous catalyst ?
a catalyst in a different physical state to the reactants
What is a homogeneous catalyst ?
a catalyst in the same physical state as the reactants
Explain how the use of a catalyst reduces energy demand and benefits the environment.
- lower temperature can be used
- so less fossil energy needed and less fossil fuels used
- so it is cheaper and less CO2 is released
What is the area under the curve in a Boltzmann distribution ?
the total number of molecules
Why does a Boltzmann distribution curve never cross the x-axis after (0,0) ?
because there is no maximum energy for a molecule
Where does the peak move to in a Boltzmann distribution curve when the reaction happens at a higher temperature ?
- the peak moves to a higher energy with a lower height (down and to the right)
What needs to happen for a dynamic equilibrium to take place ?
- reaction needs to happen in a closed system
- the rate of the forward reaction needs to equal the rate of the backwards reaction
- the concentration of reactions and products must stay the same throughout the reaction
What is le Chatelier’s principle ?
when a system in equilibrium is subjected to a change the system adjusts itself to minimise the change
