22. a Nuclear reactions are reactions, involving atomic nuclei, that have been i
ID: 700273 • Letter: 2
Question
22. a
Nuclear reactions are reactions, involving atomic nuclei, that have been induced by external stimuli (e.g. high temperatures, neutron bombardment, irradiation). They are therefore not spontaneous.
By contrast, nuclear decay (in which a nucleus splits into two or more nuclei) is spontaneous and random.
The difference between a nuclear reaction and nuclear decay is only in the initiation of the action.
An alpha particle can be emitted both through stimulation (in a nuclear reaction) or spontaneously (in alpha decay).
Nuclear reactions can be divided into two broad categories:
nuclear fusion (merging two small atoms)
nuclear fission (splitting one big atom)
The number of protons and neutrons (and thus of nucleons) and the total energy-mass are conserved in both nuclear reactions and nuclear decay. The rest mass of the individual particles is not conserved.
The conservation of the number of protons and neutrons is related to the nature of the strong force that preserves the intrinsic properties of a nucleon.
23. a
24. b
During the first 27 minutes, ½ of the nuclei decay. Now we have 32 nuclei of a radioactive element. During the second 27 minutes, ½ of the 32 nuclei decay. Now we have 16 nuclei of a radioactive element. During the third 27 minutes, ½ of the 16 nuclei decay. Now we have 8 nuclei of a radioactive element. During the fourth 27 minutes, ½ of the 8 nuclei decay. Now we have 4 nuclei of a radioactive element.
The total time for four half lives = 4 * 27 = 108 minutes
25. c
26. d
23% w/w LiCl means
23 g LiCl in (23g LiCl + 77 g H2O).
mols LiCl = 23/molar mass LiCl =0.55
mols H2O = 77/molar mass H2O =4.27
mole fraction of water = 4.27/4.82
Explanation / Answer
-22, which of the following is characteristic of a nuclear reaction? L Electrons II. Elements are converted from one to another III. Reaction rates are typically not affected by catalysts IV. Atoms are rearranged by the breaking and forming of chemical bonds in atomic orbitals are involved in the breaking and forming of bonds a. I and I b. I. II. and III c. Ill and IV d. II and III e I.II. I.and Iv 23. List the number of protons, neutrons, and nucleons (protons+ neutrons), in that order, for an isotope with the symbol: a a. 56, 81, 137 b. 81, 56, 137 c. 56, 137, 193 d. 137, 56, 193 e. 81, 137,218 -24, The half life for a first order reaction is 27 min. How long will it take for 4 half lives to a. 53,000 min b. 108 min c. 81 min d. 260 min Not enough information given e. 25. For which type of titration will the plH be basic at the equivalence point? a. Strong acid vs. strong base b. Strong acid vs. weak base c. Weak acid vs. strong base. d. All of the above. e. None of the above. 26, A 23.0% by mass LiCl solution is prepared in water, what is the mole fraction of the water? a. 0.113b0.127 c.0.873 d. 0.887 e. 0.911 6 of 11
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