Rates Flashcards
What is the rate of reaction?
the rate of change of the conc of a reactant or product with time
What is the units for ROR?
moldm-3 s-1
How can a reaction be followed?
measuring the change in mass as a function of time
measuring how the tot vol of gas produced evolved varies with time
measuring pH as a function of time
How do you find the ROR from a graph?
it is the gradient
What is the collision theory?
particles have to be physically next to one another in order to react. If they are moving aroubnd randomly in a gas/solution, this will happen as a result of chance of collisions
How does the ROR depend on the collison theory?
the frequency of collisions between particles
the probability that a collision will successfully result in a reaction
What is the relationship between ROR and conc/ pressure?
ROR increases as the conc/ pressure increases
Why does ROR increase with increase in conc?
the particles are closer together and so collide more often
What is the activtion energy?
the minimum amount of energy the particles must have for a reaction to occur
What is the relationship between the ROR and the Ea?
the higher the activation energy the lower the probability that colliding molecules will have sufficient energy to react = ROR is slower
What does the boltzmann distribution show?
the relative number of particles that have particular energies
What does the area after the Ea on the boltzmann diagram show?
the proportion of molecules that have enough energy to react when they collide
What is the relationship between the temp and ROR?
increasing temp increases ROR
What are the 2 reasons why increased temp increases ROR?
- as temp increases there are more particles that have an energy greater than Ea
- molecules are moving around faster = collide more often
What does the bolzmann distribution look like with increased temp?
curve flattens
How does a catalyst speed up ROR?
provides an alternative pathway of lower Ea
How does the boltzmann distribution change with a catalyst?
the Ea is reduced so moves to the left of the graph
what is a homogeneous catalyst?
the catalyst is in the same phase as reactants
what is a heterogeneous catalyst?
catalyst in a different phase from the reactants
What is an eg of heterogenous catalyst?
Nickle catalyst for hydrogenation
What is an eg of a homogeneous catalyst?
Cl- catalyst in the destruction of the ozone layer
What economic importance do catalyst have?
operating at lower temps = less fuel is needed so saves in production costs
How do catalysts increase sustainability?
reduced energy deman from combustion of fossil fuels = less emission of CO2
conserves raw materials used in the reaction and reduces waste = increases atom economy and percentage yield
