18.2 quiz

Question 1

what does the size of the specific rate constant, 𝘬, indicate about the rate of a chemical reaction?

Answer 1

𝘬 is large if products form quickly; 𝘬 is small if products are formed slowly

Question 2

how do most chemical reactions progress from start to finish?

Answer 2

they usually happen in small steps called elementary reactions

Question 3

how do you use a graph of reactant concentration vs time to determine the rate of a chemical reaction?

Answer 3

𝐡𝐨𝐰 𝐭𝐨 𝐮𝐬𝐞 𝐭𝐡𝐞 𝐠𝐫𝐚𝐩𝐡: it shows how the amount of reactant decreases overtime

𝐡𝐨𝐰 𝐭𝐨 𝐝𝐞𝐭𝐞𝐫𝐦𝐢𝐧𝐞 𝐭𝐡𝐞 𝐫𝐚𝐭𝐞: the rate is found by calculating the slope; a steeper slope = faster reaction

Question 4

Consider the one-step reaction aA \to B with the following rate law:
\text{Rate} = k[A]^x
When the initial concentration of A is increased from 0.35 mol/L to 0.7 mol/L, the initial rate increases from 1.6 mol/(L·ps) to 3.2 mol/(L·ps).
1. What is the order of the reaction with respect to A?
2. What is the overall order of the reaction?

Answer 4

1. Initial concentration of A = 0.35 mol/L, Initial rate = 1.6 mol/(L·ps)
   - New concentration of A = 0.7 mol/L, New rate = 3.2 mol/(L·ps)
2. 3.2/1.6= 2

2 = (2)^x
Since 2^1 = 2, x = 1

The reaction is 𝐟𝐢𝐫𝐬𝐭 𝐨𝐫𝐝𝐞𝐫
The overall order is 𝟏

Question 5

The following reaction takes place:
NO(g) + O3(g) → NO2(g) + O2(g)
The rate law is first order in NO and O3, and second order overall.
Write the rate law for this reaction

Answer 5

𝘬[NO][O3]

Question 6

what is an elementary reaction, and how is it related to a reaction mechanism?

Answer 6

• 𝐞𝐥𝐞𝐦𝐞𝐧𝐭𝐚𝐫𝐲 𝐫𝐞𝐚𝐜𝐭𝐢𝐨𝐧𝐬 are when reactants turn into products in 1 step
• 𝐫𝐞𝐚𝐜𝐭𝐢𝐨𝐧 𝐦𝐞𝐜𝐡𝐚𝐧𝐢𝐬𝐦𝐬 are the series of steps that describes what happens during the reaction

Question 7

is an intermediate a reactant or a product? explain

Answer 7

neither!
𝐫𝐞𝐚𝐜𝐭𝐚𝐧𝐭𝐬 are the starting material
𝐩𝐫𝐨𝐝𝐮𝐜𝐭𝐬 are the final results

𝐢𝐧𝐭𝐞𝐫𝐦𝐞𝐝𝐢𝐚𝐭𝐞𝐬 are neither. they are formed during the reaction but are used up before the reaction is complete

Question 8

Look at the equation for the reaction of nitrogen oxide (NO) and ozone (O₃):

NO + O₃ → NO₂ + O₂

Do you think this is a single-step or multi-step reaction? Use what you know about collision theory to explain your answer

Answer 8

most likely a 𝐬𝐢𝐧𝐠𝐥𝐞-𝐬𝐭𝐞𝐩 reaction because:
- only two molecules (NO and O2) collide, making it simple and likely to just hapen in one step
- in collision theory, two reactants are more likely to occur in 1 step rather than needing more collisions

Question 9

Suppose the initial rate for a first-order reaction is 0.5 mol/(L·s). What is the rate when half the reactant remains? When one fourth of the reactant remains?

Answer 9

when it’s 𝐡𝐚𝐥𝐟: 0.5 / 2 = 0.25mol/(L·s)

when it’s one 𝐟𝐨𝐮𝐫𝐭𝐡: 0.5 / 4 = 0.125mol/(L·s)

Question 10

Show that the unit of the rate constant (k) for a first-order reaction is a reciprocal unit of time, such as s⁻¹

Answer 10

𝘬= 1/s

1. mol/Ls = 𝘬 x mol/L
2. divide both sides by (mol/L)
3. the mol/L cancels out, leaving 𝘬= 1/s

Question 11

Ho

Answer 11

Holmium

Question 12

Er

Answer 12

Erbium

Question 13

Tm

Answer 13

Thulium

Question 14

Yb

Answer 14

Ytterbium

Question 15

Lu

Answer 15

Lutetium

Question 16

Hf

Answer 16

Hafnium

Question 17

Ta

Answer 17

Tantalum

Question 18

first order reaction

Answer 18

the rate is directly proportional to the concentration of only 𝐨𝐧𝐞 reactant

Question 19

specific rate constant

Answer 19

• (𝘬)
• number that shows how fast a reaction happens
• it links the concentration of reactants to the rate of the reaction

Question 20

rate law

Answer 20

an expression/equation for the rate of a reaction in terms of concentration of reactants

Question 21

rate

Answer 21

speed of reaction

Question 22

[A] and [b]

Answer 22

concentrations of reactants

Question 23

x and y

Answer 23

reaction orders with respect to each reactant