Chemistry Unit 6 Flashcards
Kinetics
What is rate the reciprocal of?
Time
In a chemical reaction, as the concentration of the reactants decrease, the concentration of the products _______
Increase
When is the rate the greatest, and why is it then?
It is greatest at the start of a reaction because the concentration of the reactants is at its highest
Why would a graph showing the concentration of the products/reactants versus time plateau after a little while?
The reaction hits equilibrium and the concentrations are constant
List the five main ways to measure the rate of a reaction in a lab
- Change in volume of gas produced
- Change in mass
- Color change (spectrophotometer)
- Change in concentration
- Clock reaction
What are the two ways to measure a change in volume of gas produced?
- Use gas syringe to collect gas being produced at regular time intervals
- Collect gas over water (displacement), gas must have low solubility
What must be present in order to measure the change in volume of gas produced?
One product must be a gas
What are the two ways to measure change in concentration?
- Titration
- Conductivity - ions and charge allow for a solution to conduct
Does a decrease in number of ions mean a decrease or increase in conductivity?
Less ions means less conductivity!
What three things are listed in the collision theory?
- Particles must collide
- Particles must collide with appropriate orientation so that the reactive parts of the particles come into contact with each other
- Particles must collide with enough energy to react
Define Maxwell Boltzman Distribution and what it shows
The moving particles of a liquid or gas are not moving with the same velocity, some are moving faster and others slower. The faster they move the more kinetic energy they have. The Maxwell Boltzman Distribution shows the kinetic energy of particles
What does the area under the curve represent in a Maxwell Boltzman Distribution?
The area represents the number of particles with enough energy to react. As temp increases, the number of particles stays the same but the number of particles with more kinetic energy increases, which is why the higher temperature has a greater area.
How does the temperature affect the rate of a reaction?
Higher temperature = more particles with more kinetic energy = more effective collisions = faster rate
The rate of the reaction doubles for about every ___ degrees celsius the temp increases
10
How does the surface area affect the rate of a reaction?
More surface area = more places for collisions = faster rate
How does concentration affect the rate of a reaction?
Higher concentration = more particles to collide = faster reaction rate
What causes the initial rate of a reaction to be faster?
A greater concentration because there are more particles to collide.
If they have the same number of moles but one has a greater concentration, they will start apart but end at the same spot
As the reaction happens does the concentration of the reactants increase or decrease?
Decrease
If the two reactions have different numbers of moles of reactants, will they end at the same spot?
No, the one with more moles will be greater
How does a catalyst affect the rate of a reaction?
A catlyst increases the rate of a reaction by providing an alternative pathway
Does a catalyst cause a reaction to need more or less activation energy?
Less!
Is the catalyst ever seen in a reaction?
No!
Does a catalyst change the heat of reaction?
No!
Define reaction mechanisms
A series of simple steps involved in a reaction
What is each step of a reaction mechanism called?
An elementary step
What is molecularity?
The number of reacting species in an elementary step
What is it called if there is only one reactant in an elementary step?
Unimolecular
What is it called if there are two reactants in an elementary step?
Bimolecular
What is it called if there are three reactants in an elementary step?
Termolecular
What is an intermediate?
A product of an elementary step that is used in a subsequent step. It is NOT part of the overall reaction
In order for a set of elementary steps to be a possible mechanism for the reaction, they must what?
Add up to the overall equation
The ____ step must give a rate law consistent with the ________ rate law
Slow; Experimental
True or false: An intermediate can be isolated during the reaction
True!
When is the transition state and can it be isolated?
The state exists as bonds are broken and formed. It cannot be isolated during the reaction
Define Rate expression/Rate law
Mathematical expression to describe the relationship between the concentration of reactants and the rate of a reaction
What is the formula for rate law?
Rate = K [A]^m [B]^n [C]^p…
True or false: the k constant is specific to the reaction
True
What are the name of the exponents in the rate law formula?
They are the order of the reaction with respect to that specific reactant
K, m, n and p are determined from what?
Experimental data
What is the only thing which will change the K constant?
Temperature
How do you find the overall order of the reaction?
Add up the exponents
How does the concentration affect the rate of reaction for a zero order?
It doesn’t
How does the concentration affect the rate of reaction for a first order?
It is directly proportional
How does the concentration affect the rate of reaction for a second order?
The rate is proportional to the square root of the concentration
Define the rate of a chemical reaction
The change in concentration of reactants or products per unit of time
What do we know about the areas under two curves in a Maxwell-Boltzmann energy distribution?
They are equal
What are the labels of the axes on a Maxwell-Boltzmann energy distribution?
X-axis: Kinetic Energy
Y-axis: Number of Particles
If you increase the pressure on a gaseous reaction, which side will it favor more?
It will favor whichever side has more moles
What does the Arrhenius Equation do?
It uses the temperature dependence of the rate constant (k) to determine the activation energy for a reaction
What does the Arrhenius Constant/Frequency Factor indicate?
The frequency of collisions and the probability that collisions have proper orientation for the reaction to occur
What is the Arrhenius Equation?
K = A e ^ (-Ea/RT)
What is the logarithmic form of the Arrhenius Equation?
ln K = -Ea/RT + ln A
What’s the equation for activation energy that includes the slope created through the graph of the arrhenius equation?
Ea = -slope x 8.31 J/molK
What are the x and y axis labels of the logarithmic arrhenius equation?
X: 1/T (units: 1/K)
Y: ln K
Do reactions with higher activation energy have a steeper or flatter slope?
Steeper
How do you find the activation energy through the rate constant and temperature?
- You find the ln or the rate constant and the 1/Temperature for every values
- You then take the first and last numbers and use the slope formula (change in Y/change in X)
- Using the formula Ea = -slope x 8.31 J/moleK you find the activation energy in Joules
- Divide by 1000 to find in KJ
These are the steps
Describe what the graph of concentration vs time for a zero order looks like
time is x-axis, concentration is y
A direct decrease
Describe what the graph of rate vs concentration for a zero order looks like
A straight horizontal line
Describe what the graph of concentration vs time for a first order looks like
Starts at the top and then exponentially decreases
Describe what the graph of rate vs concentration for a first order looks like
A direct increase
Describe what the graph of concentration vs time for a second order looks like
Starts at the top and exponentially decreases, is steeper than the first order
Describe what the graph of rate vs concentration for a second order looks like
A slightly curved increase
