University:
Florida Gateway College
Course:
CHM 2045 | General Chemistry I
Academic year:

2024
Views:

298

Pages:

2
Author:

boleertf

CHEMISTRY Question 8 Total Score 8 points 8. The decay of the radioisotope I-131 was studied in a laboratory. I-131 is known to decay by beta ( −01 e ) emission. (a) Write a balanced nuclear equation for the decay of I-131. 131 53 I Note: “β” for 0 −1 e → 131 54 Xe + 0 −1 e 1 point for correct equation is acceptable (b) What is the source of the beta particle emitted from the nucleus? A neutron spontaneously decays to an electron and a proton. 1 point for identifying a neutron as the source of the beta emission The radioactivity of a sample of I-131 was measured. The data collected are plotted on the graph below. (c) Determine the half-life, t1/2 , of I-131 using the graph above. The half-life is 8 days. That is the time required for the disintegration rate to fall from 16,000 to one-half its initial value, 8,000. 1 point for half-life CHEMISTRY Question 8 (d) The data can be used to show that the decay of I-131 is a first-order reaction, as indicated on the graph below. (i) Label the vertical axis of the graph above. The label on the y-axis should be ln or log one of the following: disintegrations or moles or atoms or [I-131] or disintegration rate. 1 point for correct label on y-axis (ii) What are the units of the rate constant, k , for the decay reaction? From the graph, the units on the rate constant are days−1 (Units of time−1 is acceptable) 1 point for correct units (iii) Explain how the half-life of I-131 can be calculated using the slope of the line plotted on the graph. The slope of the line is −k. The slope is negative, so k is a positive number. The half-life can then be calculated using the 0.693 relationship t1/2 = k . 1 point for indicating slope is k 1 point for half-life equation (d) Compare the value of the half-life of I-131 at 25°C to its value at 50°C. The half-life will be the same at the different temperatures. The half-life of a nuclear decay process is independent of temperature. 1 point

Chem Kinetics Half-life Answers

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