Mechanisms
True/False
Most reactions occur by one-step mechanisms
False, many reactions occur in multi-step mechanisms
True/False
The rate law can be deduced from examination of the overall balanced equation of the reaction.
False, Rate law is experimentally observed.
If the half-life of a reaction is independent of concentration, what is the order of the reaction?
First
After mixing 10.00 g of compound A with 20.00 g of compound B, its is found that the mole fraction of compound A is 0.400. What's the mole fraction of compound B
0.600
Magnesium hydroxide and hydrochloric acid
Write molecular equation
MgOH + HCl -> H2O + MgCl
Step 1: H2O2 + I- -> H2O + OI-
Step 2: H2O2 + OI- -> H2O + O2 + I-What is the catalyst and intermediate?
Catalyst I- Intermediate OI-
In the rate law, Rate = k[X]2[Y], what are the units of K
M2s-1
After 44 minutes, a sample of 4419K is found to have decayed to 25 percent of the original amount present. What is the half−life of 4419K?
22 minutes
What is the percent by mass of solution when 65.3 g of the compound KNO3 (molar mass=101 g/mole) is placed in 161 g of water (molar mass=18.0 g/mole)?
28.86%
Potassium chromate and calcium chloride
Write Molecular equation
K2CrO4 + 2CaCl → Ca2CrO4 + 2KCl
How does a catalyst increase the rate of a chemical reaction?
a)By changing the magnitude of the enthalpy change.
b)By providing a pathway for the reaction that has a lower activation energy.
c) By decreasing the potential energy of the products
d) By increasing the potential energy of the reactants
e).By giving energy to the reactants so more of them have energies greater than the activation energy
B
What plot will yield a straight line for a first order reaction and what will the slope be?
m=-k and ln[A] vs. time
A sample of radioactive cadmium has a half life of 15 days. If you have a sample that originally weighed 40 g and later weighs 2.5 g. How much time elapsed between the initial and final masses?
60 days
What is the mole fraction of CaCl2 (molar mass=111 g/mole) when 3.75 g of it is placed in 10.1 g of water (molar mass=18.0 g/mole)?
0.0568
Ammonium phosphate and zinc nitrate
Write Molecular equation
(NH4)3PO4 + 3ZnNO3 → Zn3PO4 + 3NH4NO3
5Br- + BrO3- + 6H+ → 3Br2 + 3H2O
What is the effect of increasing [H+] in this reaction at a constant temperature?
a.) The value of the rate constant increases.
b.) The potential energy of the products decreases.
c.) The potential energy of the activated complex decreases.
d.) The number of collisions between H+ and Br− ions increases.
e.) The number of collisions between H+ and Br− ions decreases
d) Increasing concentration always increases collision frequency, but may not always increase rate if a reaction is zero order with respect to the increasing reactant.
Expirements during a recent summer on a number of fireflies showed that the average interval between flashes of individual insects was 16.3 s at 21 C and 13.0 s at 27.8 C. Hint:(to calculate k, use 1 flash = k x seconds
What is the activation energy that controls the flashing?
24.1 kJ/mole
Tritium decays by a first-order process that has half-life of 12.5 years. How many years will it take to reduce the radioactivity of a tritium sample to 15% of it original value?
34 yrs
What is the molarity of sodium chloride in solution that is 13.0% by mass sodium chloride and that has adensity of 1.10 g/mL?
2.45
Lithium hydroxide and barium chloride
Write Molecular equation
2LiOH + BaCl2 -> 2LiCl + Ba(OH)2
step 1: X4+ + Y2+→ X3+ + Y3+
step 2: X4+ + Y3+→ X3+ + Y4+
step 3: Y4+ + Z+ → Z3+ + Y2+
The catalyst in this process is
A certain reaction has the following general form
aA -> bB
At a particular temperature and [A]0= 2.00x10-2 M, concentration versus time data were collected for this reaction, and a plot of ln[A] versus time resulted in a straight line with a slope value of -2.97x10-2 min-1.
What is the rate law, integrated rate, and rate constant? Whats the half life? How much time is required for A to become 2.50x10-3M?
rate=2.97x10-2[A],
ln[A] = -2.97x10-2t +ln[2.00x10-2],
k= 2.97x10-2
23.3 min
70.0 min
The half-life of 99Tc is 6.00 hours. If it takes exactly 12.00 hours for the manufacturer to deliver a 99Tc sample to a hospital, how much must be shipped in order for the hospital to receive 10.0 mg?
If delivery takes 12 hours, that’s two half lives. To have 10 mg remaining, work backwards 10 << 20 << 40 mg must be sent.
You have a solution which is 45.6% by mass isopropyl alcohol (MM = 60.11 g/mol) in water. The density of this solution is 0.905 g/mL.
A)What is the molality of the isopropyl alcohol in the solution?
B)What is the molarity of the isopropyl alcohol in the solution?
C)What is the mole fraction of the isopropyl alcohol in the solution?
A)13.9
B)6.87 M
C)0.201
Sodium chloride and lead II nitrate
2NaCl + Pb(NO3)2 -> PbCl2 + 2NaNO3