Topic 9: Kinetics I Flashcards
What are the two conditions required for particles for a reaction to take place?
- they collide in the right direction. they need to be facing each other the right way
- they collide with at least a certain minimum amount of kinetic energy (activation energy)
Why is activation energy needed to start the reaction?
- particles need this much energy to break the bonds to start the reactions
Draw a Maxwell-Boltzmann Distribution graph and explain
- the curve starts at (0,0) because no molecules have zero energy
- a few molecules are moving slowly
- most molecules are moving at a moderate speed so their energy are in the middle range
- the area on the right represent the molecules that have at least the activation energy. these are the only ones that can react
What happens when you increase the temperature?
- the particles will on average have more kinetic energy and will move faster
- so a greater proportion of the molecules have at lest the activation energy to be able to react
- this changes the shape of the Maxwell-Boltzmann distribution curve by pushing its to the right
- molecules have more kinetic energy mean they’ll collide more frequently so rate of reaction increases
Draw a Maxwell-Boltzmann Distribution graph when temperature is at 25 and at 35
GOOOOO
What does increasing the concentration do to rate of reaction?
- speeds up rate of reaction
- they’re will be more particles in a given volume of the solution, so particles will collide more frequently
- more frequent collisions, means more chances to react
What does increasing the pressure do to rate of reaction?
- if any of reactants are gases, increasing the pressure will increase rate of reaction - at higher pressure, there are more particles in a given volume of gas, which increases the frequency of successful collisions
What do catalysts do to rate of reaction?
- catalysts lower the activation energy by providing a different way for the bonds to be broken and remade
- more particles will have enough energy to reaction - more successful collisions
What is an equation for rate of reaction?
- rate of reaction = amount of reactant used or amount of product formed / time taken
What is the definition of a catalyst?
- a catalyst increases the rate of a reaction by providing an alternative reaction pathway with a lower activation energy, so a greater proportions of collisions result in a reaction
- the catalyst is chemically unchanged at the end of the reaction
Why are catalysts good?
- they don’t get used up so you only need a small amount
- they do take part in the reaction, but they’re remade at the end
What is a heterogenous catalyst?
- a heterogenous catalyst is one that is in a different phase from the reactants i.e. different physical state
- the reactions happens on the surface of the heterogenous catalyst
- so increasing surface area increases the number of molecules that can react at one time, increasing rate of reaction
Show the effect pf heterogenous catalysts by drawing an reaction profile diagram
- they lower the activation energy of the reaction
How do solid heterogenous catalysts work?
- reactant molecules arrive at the surface and bond with the solid catalyst. this is call adsorption
- the bonds between the reactant’s atoms are weakened and break up. this forms radicals. these radicals then get together and make new molecules
- the new molecules then detach from the catalyst. this is desorption
What are homogenous catalysts?
- they are in the same physical state as the reactants
- use is an aqueous catalyst for a reaction between two aqueous solutions
