[CHEM] Unit 11- Kinetics Flashcards
In order to react, reactants need to have:
Effective collisions
Two things are needed for effective collisions:
1) Enough energy
2) Proper orientation (based on polarity)
To react quickly, ionic reactants need to be in the ___ phase
Aqueous (aq)- solid ionic reactants don’t break apart
Covalent reactants typically have ___ bonds to break and so react ___
More, slowly
Temperature is a measure of the:
Average kinetic energy of the particles
A high temp leads to ___ energy, and so ___ particles will collide with sufficient energy
Higher, more
A high temp also leads to:
Particles moving faster, and so more total collisions will occur
How does concentration affect rate?
Higher concentration=faster rates because there are more total collisions
Pressure only affects ___ reactants
Gas
How does pressure affect rate?
Pressure is caused by the particles colliding with the walls of the container- more collisions will walls will mean more collisions between particles
How does surface area affect rate?
Reactions only occur at the surface where the reactants are in contact; therefore, as surface area increases, there will be more total collisions (and in turn more effective collisions)
Trick to remember: Sugar cubes vs powdered sugar
How does one increase surface area?
For solids, grind them into small pieces
For liquids, stir
How does a catalyst affect rate?
Catalysts reduce the required energy for an effective collision, thereby making more (already existing) collisions effective
T/F: A catalyst is used up during a reaction
F
Endothermic=
Heat put in (heat is a reactant)
Breaking/forming a bond is endothermic
Breaking!
Exothermic=
Heat is released (heat is a product)
Breaking/forming a bond is exothermic
Forming!
On a PED, if a reaction is endothermic, the ΔH is:
Positive
On a PED, if a reaction is exothermic, the ΔH is:
Negative
ΔH is:
Heat of reaction, or change of enthalpy
How does one tell if a PED is exothermic or endothermic?
Products have more energy= Endothermic
Products have less energy= Exothermic
The activated complex is:
The peak of potential energy; a state between reactants and products
Activation energy is:
The difference between the PE of the activated complex and the PE of the reactants
ΔH is calculated by:
PE of products - PE of reactants
If a catalyst is added to a PED, what changes?
The activation energy is reduced, and the PE of the activated complex is also reduced.
ΔH DOES NOT CHANGE
In a reverse PED, the products become the ____ and the reactants become the ___
Reactants, products
To find the activation energy of a reverse PED, one needs to
FInd the different between the PE of the products and PE of the activated complex
T/F: In a reverse reaction/PED, the ΔH changes
T
T/F: The reverse reaction is always the opposite of the normal reaction (in terms of endothermic vs exothermic)
T
When using Table I for changes in enthalpy, if the coefficients of the reactants/products are changed, then:
The ΔH must be changed accordingly (doubled, halved, etc)
In terms of enthalpy (ΔH), nature tends to favor ___ energy- ie ___thermic
Low, exo
Entropy is:
Randomness or disorder
In terms of entropy (ΔS), nature tends to favor ___ entropy
Higher
The phase lowest in entropy is:
Solid
The phase(s) highest in entropy is/are:
Gas and aq
The phase in the middle in terms of entropy is:
Liquid
One way to increase entropy is to:
Mix the subtances
Higher temperature=___ ΔH
Higher
The equation for Gibbs Free Energy is:
ΔG= ΔH- T(ΔS)
TEMPERATURE HAS TO BE KELVIN!!
For a reaction to be spontaneous, the ΔG has to be:
Negative
A positive ΔH (___) and negative ΔS means:
Endo; the reaction is ALWAYS positive- therefore it is never spontaneous
A negative ΔH (___) and positive ΔS means:
Exo; the reaction is ALWAYS negative- therefore it is always spontaneous
Both a negative ΔH and ΔS means:
The reaction is only spontaneous at LOW temperatures
Both a positive ΔH and ΔS means:
The reaction is only spontaneous at HIGH temperatures
