What is Bismuth – Properties of Bismuth Element – Symbol Bi
The pressure at which vaporization boiling starts to occur for a given temperature is called the saturation pressure. Adding a heat will convert the solid into a liquid with no temperature change.
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The melting point of a substance depends on pressure and is usually specified at standard pressure. When considered as the temperature of the reverse change from liquid to solid, it is referred to as the freezing point or crystallization point. When a given amount of heat is added to different substances, their temperatures increase by different amounts. Latent heat is the amount of heat added to or removed from a substance to produce a change in phase.
When latent heat is added, no temperature change occurs. The enthalpy of vaporization is a function of the pressure at which that transformation takes place. The liquid phase has a higher internal energy than the solid phase. This means energy must be supplied to a solid in order to melt it and energy is released from a liquid when it freezes, because the molecules in the liquid experience weaker intermolecular forces and so have a higher potential energy a kind of bond-dissociation energy for intermolecular forces.
Intermolecular Forces: Review
Boron 5 B. Carbon 6 C. Neon 10 Ne. Sulfur 16 S. Argon 18 Ar. Iron 26 Fe. Cobalt 27 Co. Nickel 28 Ni. Copper 29 Cu. Zinc 30 Zn. Gallium 31 Ga. Arsenic 33 As. Bromine 35 Br.
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Yttrium 39 Y. Silver 47 Ag. Indium 49 In. Tin 50 Sn. Iodine 53 I. Xenon 54 Xe. Iridium 77 Ir. Gold 79 Au. Thallium 81 Tl.
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Lead 82 Pb. Radon 86 Rn. Cerium 58 Ce. Erbium 68 Er. In all three series, the end-product is a stable isotope of lead. The neptunium series, previously thought to terminate with bismuth, terminates with thallium Radioactive decay follows first-order kinetics.
Since first-order reactions have already been covered in detail in the kinetics chapter, we will now apply those concepts to nuclear decay reactions. For example, cobalt, an isotope that emits gamma rays used to treat cancer, has a half-life of 5. In a given cobalt source, since half of the nuclei decay every 5. Note that for a given substance, the intensity of radiation that it produces is directly proportional to the rate of decay of the substance and the amount of the substance. This is as expected for a process following first-order kinetics.
Thus, a cobalt source that is used for cancer treatment must be replaced regularly to continue to be effective. Since nuclear decay follows first-order kinetics, we can adapt the mathematical relationships used for first-order chemical reactions. We generally substitute the number of nuclei, N , for the concentration. If the rate is stated in nuclear decays per second, we refer to it as the activity of the radioactive sample.
The rate for radioactive decay is:. Example 1 applies these calculations to find the rates of radioactive decay for specific nuclides. Rates of Radioactive Decay decays with a half-life of 5. Solution a The value of the rate constant is given by:. Rearranging the first-order relationship to solve for this ratio yields:. The fraction of that will remain after Or put another way, Substituting this into the equation for time for first-order kinetics, we have:.
Check Your Learning Radon, , has a half-life of 3.
How long will it take a sample of radon with a mass of 0. Because each nuclide has a specific number of nucleons, a particular balance of repulsion and attraction, and its own degree of stability, the half-lives of radioactive nuclides vary widely. For example: the half-life of is 1. The half-lives of a number of radioactive isotopes important to medicine are shown in Table 2 , and others are listed in Appendix M.
This process is radiometric dating and has been responsible for many breakthrough scientific discoveries about the geological history of the earth, the evolution of life, and the history of human civilization. We will explore some of the most common types of radioactive dating and how the particular isotopes work for each type. The radioactivity of carbon provides a method for dating objects that were a part of a living organism. This method of radiometric dating, which is also called radiocarbon dating or carbon dating, is accurate for dating carbon-containing substances that are up to about 30, years old, and can provide reasonably accurate dates up to a maximum of about 50, years old.
Carbon forms in the upper atmosphere by the reaction of nitrogen atoms with neutrons from cosmic rays in space:. All isotopes of carbon react with oxygen to produce CO 2 molecules. The ratio of to depends on the ratio of to in the atmosphere.
The natural abundance of in the atmosphere is approximately 1 part per trillion; until recently, this has generally been constant over time, as seen is gas samples found trapped in ice. The incorporation of and into plants is a regular part of the photosynthesis process, which means that the ratio found in a living plant is the same as the ratio in the atmosphere.
But when the plant dies, it no longer traps carbon through photosynthesis. Because is a stable isotope and does not undergo radioactive decay, its concentration in the plant does not change. Thus, the ratio gradually decreases after the plant dies. The decrease in the ratio with time provides a measure of the time that has elapsed since the death of the plant or other organism that ate the plant. Figure 7 visually depicts this process. For example, with the half-life of being years, if the ratio in a wooden object found in an archaeological dig is half what it is in a living tree, this indicates that the wooden object is years old.
Highly accurate determinations of ratios can be obtained from very small samples as little as a milligram by the use of a mass spectrometer. Visit this website to perform simulations of radiometric dating. Radiocarbon Dating A tiny piece of paper produced from formerly living plant matter taken from the Dead Sea Scrolls has an activity of If the initial C activity was Therefore, the Dead Sea Scrolls are approximately years old Figure 8.
Check Your Learning More accurate dates of the reigns of ancient Egyptian pharaohs have been determined recently using plants that were preserved in their tombs. There have been some significant, well-documented changes to the ratio. The accuracy of a straightforward application of this technique depends on the ratio in a living plant being the same now as it was in an earlier era, but this is not always valid.
Due to the increasing accumulation of CO 2 molecules largely in the atmosphere caused by combustion of fossil fuels in which essentially all of the has decayed , the ratio of in the atmosphere may be changing. This manmade increase in in the atmosphere causes the ratio to decrease, and this in turn affects the ratio in currently living organisms on the earth.
Fortunately, however, we can use other data, such as tree dating via examination of annual growth rings, to calculate correction factors.
With these correction factors, accurate dates can be determined. In general, radioactive dating only works for about 10 half-lives; therefore, the limit for carbon dating is about 57, years. Radioactive dating can also use other radioactive nuclides with longer half-lives to date older events. For example, uranium which decays in a series of steps into lead can be used for establishing the age of rocks and the approximate age of the oldest rocks on earth. Since U has a half-life of 4. In a sample of rock that does not contain appreciable amounts of Pb, the most abundant isotope of lead, we can assume that lead was not present when the rock was formed.
Therefore, by measuring and analyzing the ratio of UPb, we can determine the age of the rock. This assumes that all of the lead present came from the decay of uranium If there is additional lead present, which is indicated by the presence of other lead isotopes in the sample, it is necessary to make an adjustment. Potassium-argon dating uses a similar method. K decays by positron emission and electron capture to form Ar with a half-life of 1.
If a rock sample is crushed and the amount of Ar gas that escapes is measured, determination of the ArK ratio yields the age of the rock.