lecture 7 thermo Flashcards
Thermodynamics tells us what?
Whether a reaction can occur spontaneously or not
True or False? Thermodynamics tells us how fast spontaneous reactions will occur
False
Chemical kinetics is the study of what?
Reaction rates
Why is having info about rates of reactions important?
For reasons such as knowing the effects of pollutants on the environment, the ripening rates of fruits, and the degrations rates of food and pharmaceuticals ect
Measuring reaction rates can give information about what?
Reaction mechanisms aka the sequence of steps that give the overall reaction
Knowledge and understanding of reaction mechanisms is important why?
For the understanding of treatment of disease, industrial processes, and reactions in the atmosphere (climate change) e.c.t
True or False? A reaction involving more than two species is highly unlikely to occur in a single step
True
True or False? Reactions between two species will always occur in a single step
False, they may not always
Reaction mechanisms are what?
The sequence of elementary steps by which the overall reaction occurs.
What is an elementary step?
A single step
What is the slow step of a multi-step reaction?
The rate determining step which controls the overall reaction rate.
Rates of a chemical reaction are always what?
Positive
Rate can be measured by what?
- Rate of appearance of a product = delta conc of product / delta time
- Rate of appearance of reactant = delta conc of reactant / delta time
True or False? The rates of appearance of products and dissapearance of reactants are related.
True
The rates of most reactions are found to depend on what?
The concentration of the reactants
The higher the conc of reactants in a reaction what?
The higher the frequency of successful collisions therefore the higher the reaction rate.
What do rate equations (rate laws) give?
The relationship between the conc of reactants and the rate of the reaction
What does k stand for?
Rate constant (or rate coefficient)
What is the generic reaction for rate equations?
aA + bB > xX + yY
Rate = k[A]m[B]n
M does not necessarily = A and n does not necessarily = B
k depends on what?
T so is calculated for a particular T
The larger k is, is the reaction faster or slower?
The reaction is faster
The powers m and n in the rate equation give what?
The order with respect to that reactant
What does 0 order mean?
This means a reactant doesn’t appear in the rate law
How do you calculate the total reaction order?
m + n
Any number to the power of 0 = what?
1
For k (rate constant) what is the order for A and B and what is the overall reaction order.
Order in A = 0
Order in B = 0
Overall order = 0
For k[A] (rate constant) what is the order for A and B and what is the overall reaction order.
Order in A = 1
Order in B = 0
Overall order = 1
For k[A][B] (rate constant) what is the order for A and B and what is the overall reaction order.
Order in A = 1
Order in B = 1
Overall order = 2
For k[A]2[B] (rate constant) what is the order for A and B and what is the overall reaction order.
Order in A = 2
Order in B = 1
Overall order = 3
What does the reaction order determine?
The units of the rate constant (k)
What are the units for a second order reaction?
L mol-1 s-1
What are the units for a zero order reaction?
mol L-1 s-1
What are the units for a first order reaction?
s-1
What are the units for a third order reaction?
L2 mol 2- s-1
