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Flashcards in Unit 2.5 Deck (62)
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reaction rate

change in concentration of a reactant or product per unit time


rate as time goes on

should decrease and be as close to 0 as possible (reaction is "finished")


instantaneous rate vs. average rate

average rate: just the slope of the change in reactant over time

instantaneous rate: shows rate at a certain point in time


rate law

shows how the rate depends on the concentrations of reactants


why don't products appear in the rate law?

the concentrations of the products do not appear in the rate law because the reaction rate is being studied under conditions where the reverse reaction does not contribute to the overall rate


integrated rate law

shows how concentration depend on time


how to measure the rate of reaction of a gas

- water displacement measures the volume of H2/ the rate that the volume changes is equal to the rate that the moles change which can give you the concentration/time
- with concentration measuring probes
- can measure the rate that the mass of a solution goes down by a scale


how to measure rate of reaction when solid is the limiting reagent

measures the mass/time which can be moles/ time


how to measure rate of reaction when acid/base

measure pH to translate to concentration of H+. as the concentration of H+ shows how much more acidic/basic a solution is getting


how to measure rate of reaction when coloured compound

measure the rate that the colour disappears/appears (qualitative) or measure using a colorimeter


how to measure rate of reaction when opaque

this is also relative using the disappearing cross experiment


rate of appearance/disappearance

when calculating the rate of change of the reactants disappearing, a negative sign is added to make the rate positive


how does rate of reaction make sense

10 mol/s means 10 moles of reactions occur each second, not that 10 moles of chemical actually react. 6.02 x 10^23 times molecules number of reactions



contains al the factors such as temperature, steric factor, reactivity etc. and the units can vary



shows how much of an effect changing the concentration of one variable has on the rate

ex. order 2 is doubled
= quadrupled reaction


overall order

sum of the exponents. a higher total order means more dependent/sensitive reaction to concentration


when given the concentration of a reactant and the eqn

don't multiply the concentration by the coefficient!


initial rate

the initial rate at which the reactants combine
experimentally: measure the instantaneous rate at t=0


nuclear decay

first order reaction


collision theory

molecules must collide to react however majority of collisions do not lead to a reaction


collision theory concentration

rate increases as the concentration of reactants increase


transition state/activated complex

bonds go through a transition state. the species at the transition state is called the activated complex. this is very unstable


activation energy

reactants must collide with enough energy to form the activated complex



at high temperature means that the molecules have a greater average kinetic energy which means the collision will have more energy to overcome the activation energy


steric factor

A, a number that represents the likelihood that a collision occurs with the right geometry.

decreasing the size, increases the rate of reaction
increases the surface area available for collisions to take place


reaction mechanism

the process by which a reaction occurs


each collision in a mechanism is called

elementary step


elementary steps

- can be uni or bimolecular (1 or 2 molecules reacting)


rate determining step

the slowest elementary step determines the rate of the overall reaction
- the order is the coefficient since each reactant is the coefficient


a valid mechanism

1. sum of elementary steps must give the overall reaction
2. the rate law based on the RDS must be consistent with the experimental rate law
3. no elementary step includes more than 2 reactants