physical chem; kinetics Flashcards
what is the collision theory?
states that for a chemical reaction to take place, particles need to collide with correct orientation & enough KE
how does ineffective collision affect a chemical reaction?
particles would bounce off without causing a chemical reaction
what is the rate of reaction?
the change of conc/amount of a reactant or product per unit time
state what happens when reaction rate increases
when more collisions take place the no.of particles with energy greater than Ea increases
what is activation energy?
it’s the minimum amount of energy required to required for reaction to occur
how does Ea affect chemical reactions?
for a reaction to take place particles need to overcome Ea
what is a catalyst & how does it affect the reaction rate?
a catalyst is a substance that increases the rate of reaction without being used up by providing an alternative pathway
how is the rate of reaction calculated?
rate of reaction (mol dm-3 s-1) = change in amount of reactants or products (mol dm-3 ) ÷ time (s)
what does the maxwell boltzmann distribution show?
shows the energy in gas particles
how does temp affect rate?
when temp increases the particles gain more KE = a larger proportion of particles will have energy greater than Ea
when temp decreases = a smaller proportion of molecules will have energy greater than Ea
how are the effects of temp shown on a maxwell boltzmann distribution graph?
increased temp:
curve sits on the right
peak is lower
are under the curve is the same
area under curve beyond Ea increases
decreased temp:
curve sits on the left
peak is higher
area under curve is the same
area under the curve beyond Ea decreases
why do we get a faster rate of reaction when temp is increased?
as particles move around more at higher temps - they collide more often = reactions happen faster
how does conc affect rate?
increasing conc = increases rate
as particles closer together & collide more often - higher chance of reaction
how does pressure affect rate?
increasing pressure = increases rate
as particles are closer together & collide more often - higher chance of reaction
why are catalysts used in reactions?
to make the products faster & are used to lower the temp required for a reaction which saves energy & money
give an example of a catalyst & its features
zeolite
has large SA due to its micro pores in the pellets
how are the effects of catalysts shown on the maxwell boltzmann distribution graph?
catalysts lower the Ea so more particles have enough energy to react (dotted Ea line moves to left)
how is rate measured in experiments?
- how long it take for ppt to form
place a cross on paper & time how long it takes for the cross to disappear (ppt to form) - use same observer to reduce errors as it’s difficult to know when exactly the cross disappears - amount of mass lost
for reactions that produce gas - place reaction on balance & measure the mass loss as gas is lost
use fume cupboard if gas is harmful/toxic - vol of gas produced
measure amount of gas produced using a gas syringe over a specified time
