Chapter 13 Flashcards
Reaction Rate (relationship)
how quickly (or slowly) a reaction occurs, are positive, look at change in concentration and change in time of both reactants and products
Equations and Units of Reaction Rates
Rate = Change in concentration/change in time, molarity/t
Factors that affect reaction rates
physical states of reactants, concentration, temperature, surface area, and catalyst
How to monitor concentration change
color change, probes, pressure sensor
Initial rate
the rate of a reaction at t=0, immediately after the reactants are mixed
Instantaneous rate
reaction rate at a particular instant, determined graphically as tangential
Rate Laws
Equation that defines the experimentally determined relationship between reactant concentrations and the rate of the reaction
Reaction order
Experimentally determined number defining the dependence of the reaction rate on the concentration of the reactant –> orders
Overall reaction order
Sum of exponents of concentration terms in the rate law
Rate constant (k)
Proportionality constant that relates the rate of a reaction to the concentration of reactants
what does the rate constant depend on?
depends on specific reactions, the temperature,the presence of a catalyst etc. units depend on the specific rate law, value of k does not depend on the concentration
How to determine rate laws
method of initial rates, instantaneous rate method, integrated rate law method
Integrated rate law
mathematical expression describing the change in concentration of a reactant with time. AKA how do we get a straight line?
Half life
The time in the course of a chemical reaction during which the concentration of a reactant decreases by half
Pseudo Rate Laws
Describes a reaction in which all the reactants but one are present at such high concentrations that they do decrease significantly during the reaction; the reaction rate is controlled by the concentration of the limiting reactant –> shown by k prime
Collision theory
before reactions atoms, molecules, or ions must first collide; an effective collision between two molecules has enough energy to break bonds, activation energy occurs, orientations of colliding species also affect reaction rate
Activation energy
the minimum energy that must be supplied by collisions for a reaction to occur. energy of activation = activation energy. energy difference from reactants to the transition states at the highest point in energy in the reaction profile
Catalyst
a substance that increases the reaction rate without itself being changed by the reaction (overall). Lowers energy activation and creates new pathway
How does a catalyst work
by changing the mechanism of a chemical reaction
Catalysis may occur in the same or different phases what is this called?
Homogenous catalyst (same phase), heterogeneous catalyst (different phase)
zeroth order units and graph
mt^-1, linear m=-k
first order units and graph
t^-1, curved at first becomes linear (after ln[]) with m=-k
second order units and graph
m^-1t^-1, curved at first becomes linear (after 1/[]) with m=k
kinetics is the
area between where the concentrations cross before they go into equilibrium
If [A]=[B] (assuming A–> B) and the reaction is spontaneous (delta G = -), then
B will go above A when graphed
If [A]=[B] (assuming A–> B) and the reaction is non spontaneous (delta G+) then,
the answer is reversed and A is graphed higher than B
If reactants to products is spontaneous then what is products to reactants in regards to delta G?
Non spontaneous
Why is G important?
Tells us which way the reaction is going (reactant to products or products to reactants)
The initial rates method uses
data from the experimental table to find the rate law
Does the order of reaction matter when finding half-lives?
no if the half-life is a whole number, but if it isn’t a whole number, need to know reaction order
If a reaction has a lower activation energy then
it will have a faster reaction
Activated complex
unstable arrangement of atoms that exists momentarily at the peak of the activation energy barrier.
