Unit 1 - Kinetics Flashcards
(37 cards)
How do you calculate reaction rate?
/\ in amount of reactant or product
_/_ in Time
time is always on the bottom
What are common time units?
h - hour
min - minute
s - second
What are common rate units?
g/min (grams/minute)
mL/h (millilitres/hour)
M/min (molarity/min)
moles/s (moles/second)
When you are measuring reaction rates what is happening to the reactants and the products?
The reactants are decreasing
The products are increasing
What is a homogeneous reaction?
a reaction where all of the reactants are in the same phase. They are fast due to thorough mixing and many collisions.
What is a heterogeneous reaction?
A reaction where the reactants are in two or more different phases.
They are slow due to poor mixing and fewer collisions
What factors increase the rate of homogeneous and heterogeneous reactions?
Increasing temperature
increasing reactant concentration
adding a catalyst
the nature of the reactant
increasing the pressure
For heterogeneous reactions only
increase surface area
agitation (stirring or fanning)
How would you rank the reaction rate for different states of matter?
homogeneous reactions are faster than heterogeneous
Fastest
(aq)
(g)
(l)
(s)
slowest
(aq) is fastest because of ionic bonds
Before two molecules can react, what must happen?
They must collide with each other. There can be no reaction without a collision.
What is the collision theory? (or Kinetic Molecular Theory)
It states that molecule act as small, hard spheres which bounce off each other and transfer energy among themselves during their collisions.
What is the effect of concentration on the Collision Theory?
If the concentration increases then more collisions are possible between molecules. Therefore the rate of reaction increases.
What is the effect of temperature on the Collision Theory?
If the temperature increases then the kinetic energy of the molecule increases and the speed at which they are moving increases. Because they move faster, they collide more often and with more energy and therefore the reaction rate increases.
What is the potential energy in chemical systems?
Potential energy is directly related to the energy of the electrons in the chemical bonds, as well as the number and type of atoms in the molecules.
It is the amount of energy possessed by a system.
What is the Kinetic Energy of a system?
It is the energy a system possesses because of movement within the system.
What is bond energy?
The amount of energy required to break a bond between two atoms.
What happens to the energy when you break a bond?
Energy must be added to the bond to break it.
Cl2(g) + 243 kJ —> 2Cl(g)
What happens to energy when you form a bond?
When you form a bond, the amount of energy equal to the bond energy is released by the atoms.
2Cl(g) —-> Cl2(g) + 243kJ
What is Enthalpy? H?
The total kinetic and potential energy which exists in a system when at constant pressure
What is an endothermic reaction?
A reaction where the products have more energy than the reactants.
What is an exothermic reaction?
A reaction where the products have less energy than the reactants
What temperature would T1 be relative to T2 when looking at the Kinetic Energy curve
T1 Temperature would be lower than the T2 temperature. The average kinetic energy of molecules is slower in T1 so the reaction rate would be slower as well.
What is the rule of thumb for slow reaction rates?
Each 10°C increase in temperature doubles the reaction rate.
Look at the far right of the area under the curve….
What does the activation energy refer too?
The minimum energy required before a molecule can react.
Consider the image. What is happening at the peak of the hill?
The peak of the hill indicates the occurrence of the actual reaction. If the reactants don’t possess enough energy to react, they can only climb partway up the hill and don’t react. Molecules with insufficient energy just bounce off each other without reacting.
