Solutions +Kinetics Test Flashcards
What is kinetics?
The study of reaction rates
What is collision theory?
For a reaction to occur, reactant molecules have to collide
What does a good collision have to have?
- Enough energy to overcome activation energy
- The molecules have to hit each other with correct orientation
What happens if you increase the number of effective collisions?
The reaction rate will increase
What are the factors that affect rate (or # of effective collisions)?
- States of matter (solid, liquid, gas, aqueous) (Gas and aqueous molecules have greater surface area)
- Surface area (greater surface area means greater number of effective collisions meaning faster rate)
- Concentration (greater concentration means more effective collisions meaning faster rate)
- Temperature (greater temp. means greater speed of molecules meaning more effective collisions meaning faster rate)
- Catalysts (lower activation energy meaning more effective collisions and a faster rate)
How do you measure rate?
- By looking at changes in reactant OR product amounts over time
Ex. 2A + 1B -> 3C
A is disappearing twice as fast as B because, for every 1 molecule of B that’s used up, 2 molecules of A are used up
*Most reactions slow down over time (except 0 order reactions with constant rates)
How to measure instantaneous rate?
Take the slope of a tangent line at a certain point in time
What are reaction orders?
- Tells you how much the concentration affects the rate
- 0 order is when the concentration does not affect the rate at all
- 1st order is when the concentration affects the rate a little bit
- 2nd order is when the concentration affects the rate a lot
What is a rate law?
Expresses or quantifies how much concentration affects rate
Rate = k[ ]^x
- Reactants go inside concentration brackets
-Thereaction order (exponent x) is determined by conducting an experiment - Find the overall reaction orders by adding up all the exponents in the rate law
What are the two types of experiments used for rate laws?
- Multiple different experiments with different initial concentrations and looking at how rate was affected
- Running one experiment to completion and watch how concentration and rate change over time
If a concentration over time graph is linear, meaning the reaction does not slow down over time, what reaction order is it?
Zero order because the reduction of concentration over time did not affect the rate
If a concentration over time graph depicts a downward curve, meaning the reaction is slowing down over time, what reaction orders is it?
1st or 2nd order because the reaction is slowing down over time
What reaction order is depicting if the natural log of concentration versus time is graphed and its linear?
1st order
What reaction order is depicted if 1 over the concentration versus time is graphed and it is linear?
2nd order
What is the differential rate law for a zero order reaction?
Rate = k
What is the differential rate law for a first order reaction?
Rate = k[A]^1
What is the differential rate law for a second order reaction?
Rate = k[A]^2
What is the integrated rate law for a zero order reaction?
[A]t = -kt x [A]i
y = mx + b
(-k = slope of zero order graph line)
What is the integrated rate law for a first order reaction?
ln[A]t = -kt + ln[A]i
(-k = slope of first order graph line)
What is the integrated rate law for a second order reaction?
1/[A]t = kt + 1/[A]t
(k = slope of second order graph line)
What is the half life for first order reactions?
Constant
What is the Arrhenius Equation?
k = A x e^-Ea/RT
A = frequency factor (a measure of how many collisions have the correct orientation)
e^Ea/RT = indicates how many collisions have enough energy that is greater than the activation energy
R = 8.314 J/molK
Integrated = lmk = -Ea/RT + lnA
y = mx + b
A reaction will only happen as fast as….?
It’s slowest step (rate limiting step) (tallest hump of a PE graph)
What is an intermediate?
A part of the reaction that is produced and consumed so it looks like it was never a part of a reaction at all
A + B -> C
C + D -> E
Overall: A + B + D -> E
The intermediate is C
What is solubility?
Measured amount of solute that can dissolve in a given amount of solvent at a particular temperature and pressure
What happens to solubility when temp. increases?
Solids and liquids become more soluble and gasses become less soluble
The solubility of a gas is….
Directly proportional to the vapor pressure of the gas above the solution
What does it mean when a solution is saturated?
The max amount of solution is dissolved
What does it mean when a solution is unsaturated?
Less than the max amount of solution is dissolved
What does it mean when a solution is supersaturated?
More than the max amount of solution is dissolved. Happens when a solution is heated.
What are colligative properties?
Properties of a solvent that change depending upon how much solute is dissolved (independent of solute identity)
Vapor pressure lowering
Solvents have less vapor pressure when solutes are dissolved to become solutions
What is entropy?
Entropy is disorder. Increasing entropy is favorable.
