chapter 3 Flashcards
What are the 4 main factors that influence the rate of reaction?
- nature of reactants 2. concentration of reactants 3. temperature 4. catalysts
as time goes on the rate of a reaction generally slows down because?
because the concentration of a reactant decreases
instantaneous rate of reaction:
is the change in concentration at any one particular time
is predicting the rate at some future time possible from just the balanced equation?
no
Zero order:
rate is independent of the concentration of the reactant
first order:
rate is directly proportional to the concentration of the reactants. So it slows down as the reaction proceeds.
second order:
rate is proportional to the square of the concentration of the reactant
the order of a reaction can be determined only by what?
experiment
what are the unites for the rate constant for zero, first and second order?
zero order= M x s^-1 First order= s^-1 Second order= M^-1 x s^-1
Left to right which graph represents first order, second order and zero order.
Half life (t1/2)
is the time required for the concentration of a reactant to fall to one-half of its initial volume
all radioactive decomposition follows ——- order kinetics
first
half life in first order is independent of ———-
concentration
An increase in temperature generally results in an increase in what?
k
activation energy and activated complex:
amount of energy needed to convert reactants into the activated complex, aka transition state
the higher the activation energy, the ——– the reaction rate
slower
the exponential factor:
is a number betweeb 0 and 1 that represents the fraction of molecules that have enough energy to make it over the activation barrier on a given approach.
collision model:
a chemical reaction occurs after a sufficiently energetic collision between 2 reactant molecules.
orientation factor (p):
reacting molecules must collide in the proper oreintation for new bonds to form. Orientation is important!
Reaction Mechanism:
is the series of individual chemical steps by which an overall chemical reaction occurs.
each step in a reaction mechanism is called a what?
elementary step
Reaction Intermediates:
species that form in one step of a mechanism and are consumed in another. A reaction intermediate is not found in the balanced equation for the overall reaction but plays a key role in the mechanism.
Rate determining step or rate limiting step:
is much slower than the others. this step determines the rate of the overall reaction
Catalysis:
a substance that increases the rate of a chemical reaction but is not consumed by the reaction
what is a positive and negative catalyst?
positive catalysts speed up a reaction and negative catalysts slow down a reaction
inhbitors are a what?
negative catalyst
how do catalysts work?
by providing an alternative mechanism for the reaction
what is the difference between homogenous and heterogenous catalysts?
homogenous exists in the same phase as the reactants where as heterogenous catyalysts exists in a different phase than the reacants
they believe the ozone hole over the antartica is caused by what kind of catalyst?
heterogenous
enzymes:
biological catalysts that increase the rates of biochemical reactions
many heterogenous catalysts are deposited on high surface area supports. Why is a large surface area important for heterogenous catalysis?
heterogenous catalysysts require a large surfave area because catalysis can only happen at the surface. A greater surface area means greater opportunity for the substrate to react which results in a faster reaction.
