CHRM Chem 161 Exam 2 Questions & Answers 2024/2025
Chemical Kinetics - ANSWERS- how fast the reactants change into products occur
Reaction Rate - ANSWERSthe change in the concentrations of reactants (or products) as a function of time
Different reactions have different rates: - ANSWERSin...
Chemical Kinetics - ANSWERS- how fast the reactants change into products occur
Reaction Rate - ANSWERSthe change in the concentrations of reactants (or products) as a function of
time
Different reactions have different rates: - ANSWERSin a faster reaction (higher rate), the reactant
concentration decreases quickly, whereas in a slower reaction (lower rate), it decreases slowly
Four control factors that affect rate: - ANSWERS1) the concentrations of reactants. molecules must
collide to react
- a major factor influencing reaction rate is reactant concentration, because a reaction can occur only if a
reactant molecules collide
- reaction rate is proportional to the concentration of reactants
- rate proportional collision frequency proportional to concentration
2) their physical state - molecules must mix to collide, determines how easily the reactants mix
- more finely divided a solid or liquid reactant, the greater its surface area, the more contact it makes
with the other reactant, and the faster the reaction occurs
3) the temperature of the reaction, molecules must collide with enough energy
- temperature affects reaction rate by increasing the frequency and more importantly the energy of
collisions
- frequency of collisions: a higher temperature, collisions occur more frequently, and so more molecules
react (rate proportional to collision frequency proportional temperature)
- energy of collision: temperature affects the kinetic energy of molecules (at a higher temperature, more
sufficiently energetic collisions occur, and so more molecules react (rate proportional collision energy
proportional temperature)
4) the use of a catalyst
, Summary of Section 16.1 - ANSWERS- chemical kinetics focuses on reaction rate, the change in
concentration over time
- under a given set of conditions, each reaction has its own rate
- concentration affects rate by influencing the frequency of collisions between reactant molecules
- physical state affects rate by determining how well reactants can mix
- temperature affects rate by influencing the frequency and, more importantly, the energy of the
collisions between reactant molecules
Rate - ANSWERSa change in some variable per unit of time
- rate of motion (speed) = change in position/change in time = x2-x1/t2-t1 = delta x/delta t
For a general reaction A -----> B
- rate = - change in concentration of A/ change in time = concA2 - concA1/t2-t1
- rate = + delta[B]/delta(t)
Three types of reaction rates - ANSWERS1) average rate: the slope of the line joining two points along
the curve
2) instantaneous rate: the rate at a particular instant during the reaction, the slope of a line tangent to
the curve at any point gives the instantaneous rate at that time
3) initial rate: the instantaneous rate at the moment the reactants are mixed is the initial rate, we use
this rate to avoid a complication: as a reaction proceeds in the forwards direction, product increases,
causing the reverse reaction to occur more quickly
Summarize the reaction: aA + bB ----> cC + dD - ANSWERSRate = -1/a(delta[A]/delta t = -
1/b(delta[B]/delta t) = 1/c(delta[C]/delta t) = 1/d (delta[D]/delta t)
Summary of section 16.2 - ANSWERS- The average reaction rate is the change in reactant (or product)
concentration over a change in time, delta t. The rate slows as the reaction proceeds because reactants
are used up.
- The instantaneous rate at time t is the slope of the tangent to a curve that plots concentration vs. time.
- The initial rate, the instantaneous rate at t=0, occurs when reactants have just been mixed and before
any product accumulates.
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