Rate Graphs and Orders

Question 1

what does the graph for a zero order reactant look like on a concentration-time graph?

Answer 1

• linear negative gradient

Question 2

how do we find k for a zero order reactant on a concentration-time graph?

Answer 2

gradient = rate constant,k

Question 3

what does the graph for a first order reactant look like on a concentration-time graph?

Answer 3

• downward curve with a decreasing gradient

Question 4

how do we find k for a first order reactant on a concentration-time graph?

Answer 4

• half lives and gradients can be used in 2 different methods
• k = ln(2) divided by half life
• k = gradient divided by where the tangent was drawn

Question 5

what is a half life(t1/2)?

Answer 5

time taken for half of the reactant to be used up

Question 6

what does the graph for a zero order reactant look like on a rate-concentration graph?

Answer 6

• horizontal straight line with a zero gradient

Question 7

how do we find k for zero order reactant on a rate-concentration graph?

Answer 7

y-intercept = rate constant,k

Question 8

what does the graph for a first order reactant look like on a rate-concentration graph?

Answer 8

• straight line through the origin

Question 9

how do we find k for first order reactant on a rate-concentration graph?

Answer 9

gradient of the straight line = rate constant, k

Question 10

what does the graph for a second order reactant look like on a rate-concentration graph?

Answer 10

• produces an upward curve with an increasing gradient

Question 11

how do we find k for second order reactant on a rate-concentration graph?

Answer 11

• plot another graph of concentration squared against rate

Question 12

what is the method called when continuous measurements are taken during an experiment?

Answer 12

continuous monitoring

Question 13

what are the methods of continuous monitoring?

Answer 13

• monitoring by gas collection
• monitoring by mass loss
• monitoring rate with a colorimeter (colorimetry)

Question 14

what is the initial rates method?

Answer 14

• determines the rate at t=0
• changing the concentration of one of the reactants but keeping all the other reactants constant and the total volume

Question 15

how can we change the concentration in the initial rates method?

Answer 15

• add varying volumes of water
• but keep the total volume the same
• and all other reactants

Question 16

what is a convenient way of obtaining the initial rate?

Answer 16

clock reaction

Question 17

what is an example of the clock reaction?

Answer 17

• iodine clocks which rely on the formation of iodine
• I2(aq) = orange-brown (sodium thiosulfate removes this orange)
• so solution goes from colourless to blue-black

Question 18

what is initial rate proportional to?

Answer 18

• 1/t