Chapter 10 Flashcards
Rate of reaction new equation
Change in concentration over time of a reactant or product
Why is the initial rate of reaction the highest snd what happens as time progresses (3)
- RoR fastest at start of reaction as each reactant is at highest concentrations.
Thus due to collision theory more frequent = more successful = high RoR - RoR slows down as reaction proceeds as reactants are used up, snd concentration decreases
- once one of reactants completely used up there is no more reaction so rate is 0
What is collision theory (3 points needed)
That for a SUCCESSFUL collision to take place particles must
- collide with each other
- collide with the correct orientation
- particles have the sufficient activation energy required for the reaction to take place
May collide but if not all conditions met= won’t react
What ways does rate of reaction thus increase (can link to collision theory
- concentration / pressure
- temperature
- catalyst
- surface area to volume ratio
Concentration / pressure
- inc this = more number of particles in same volume = leads to more frequent collisions and thus more successful collisions = increase rate of reaction
- inc pressure of gas = same particles but smaller volume or more particles same volume = frequent = successful = more RoR
Temperature effect on Ror
- inc temp = more particles have more kinetic energy = more frequent collisions = successful
- also more energy = greater proportion have required activation energy = increased RoR
What two ways to measure rate reaction based on reactants and products “
If gas produced
- upturned cylinder experiment where gas pushes water
If gas however co2 or something not apropriate (as co2 dissolves in water)
- loss of mass using cotton
How to do upturned cylinder for gas produced experiment
How to do loss in mass
- just add substance, close, measure volume, add the catalyst or reactant , close quickly start timer and start measuring gas produced
- could use gas syringe
- attach string to bung for better results
2) - add acid and carbonate to flask, record Ini two mass and then at time intervals
- cotton stops stuff from coming in?
Plot graphs, and as rate proportional to mass loss or gained , that is rate
What is a catalyst
Intermediate?
Something that increases rate of reaction without being used up itself
- offers a different reaction pathway which required lower activation energy
- may form intermediates but is always regenerated at the end
Two types of catalyst?
Example
1) homogenous
- homo = same, so it is when the catalysts snd the REACTANTS have same physical state
- reacts to form intermediates, but then breaks down and product formed snd cstskysf regenerated
(Chlorine radicals in break down of ozone )
2) heterogeneous
- where catalyst and reactant state DIFFERENT
- usually solids contacting with gaseous reactants / solution
- again absorb ti surface, and then leave
(Hydration of ethene using ni )
Why catalysts good economically
Catalysts mean less temp and thus less energy thus less fossil fuel and material , and product made faster = better for environment snd profits
Better to make catalyst and firm disadvantage
Autocatslysis?
If product acts as catalyst
Reaction start slowly then increase
Explain nature of energy of moving particles and link with Boltzmann distribution curve
In moving particles (gas / liquid), some particles will have very little energy, some will have average, some will have a lot etc
- the Boltzmann distribution just models this as curve like height
- a lot of particles have medium energy, some have very high , some have very low
Features of a Boltzmann curve
Why start at origin
Area
Hits x axis again?
- no molecules have zero energy - SO STARTS AT X AXIS
- the area under the curve is = to NUMBER PARTICLES (thus with any effects , area should stay same)
- curve does not ever have a maximum energy for particles - so it NEVER HITS 0 ON X AXIS AGAIN (goes to infinity
What happens if you increase temp on Boltzmann distribution curve
(How it looks compared to before )
- peak lowers and shifts to right (as more particles have more energy on average)
- the curve from peak is higher than before, as more proportion have activation energy
How does decreasing temperature then effect Boltzmann distribution curve
- peak raises and moves to left
- the amount of particles hitting activation decrease
What happens when a catalyst is added to Boltzmann
Just the line of activation ergeht moves to left as less energy now, and thus more particles have the required energy
What happens when a reversible reaction hits dynamic equilibrium
IN A CLOSED SYSTEM
- the forward rate of reaction = backward rate of reaction
- the concentrations of reactant / product stay constant (but not mean they are the same)
This means as fast as they making products, reactants being made just as fast, that’s why concentrations stay the same , but only in a closed system
Le chatelaine principle
I’d a system in equilibrium is subjected to an external change, the position of equilibrium will move to oppose that change
Affect of concentration increase on example of dichromate orange yellow
When you add sulfuric acid, you are increasing concentration of H+ ions, so it will move to oppose and decrease these, so moved to the right side
But when adding NaOH, think, Oh ions react with H+ ions to make H20 and decrease the concentration of H+ ions, so it will oppose, and move to the left to counter
Temoertaure
Pressure
What if moles same?
Inc temp = go to endothermic side, decrease temp = go to exothermic side
Inc pressure = goes to side with fewest moles of gas to decrease pressure
If moles same , nothing happens!
What is effect of a catalyst on equilibrium system
What will it do tho and be careful
NO EFFECT, both rates speed up by same amount, so concentration same and rate stilk same
- however it will increase the rate at WHICH EQUILIBRIUM WAS ACHIEVED
- for example,e showing both cinc it will hit straight line faster
Why not use cracked conditions
Too low temp = not good rate
- too high pressure = too expensive and dangerous too
So compromise set
What does equilibrium constant tell you
What if it is 1?
The actual position of equilibrium
If it is more than 1, shows EP is at right , towards products (just have greater proportion of product)
- if it less than 1 EP at left, towards reactants
- if 1 then shows EP halfway between reactants and products
This tells you whether there are more reactants or products in a system
How to do kc
Concentration of product to the power of mol
Over
Concentration if reactant to the power of MOLE!
