If the mixing of 10 atomic %copper into a silver crystal occurs at T=1000 K (727°C), determine the change in the Gibbs free energy on a per-mole basis if the enthalpy of solution for copper into silver is 0.25 eV/atom. (b) Based upon your result, should it be possible to mix 10 atomic %copper into silver? Explain your answer, and discuss this result in comparison to Example Problem 4.8.
What will be an ideal response?
First calculate the entropy change of mixing 10 atomic %copper atoms into a silver crystal for a total of one mole of atoms. To determine the entropy of mixing the copper into the silver to obtain a total of one mole of atoms, the chemical composition values of 10 atomic %copper and 90 atomic %silver are inserted into the entropy of mixing equation. Since the problem is on a per mole basis R replaces k in the entropy of mixing equation.
(b) The Gibbs free energy to mix 10 atomic %copper into silver at 1000 K is negative, thus this should happen spontaneously. It is possible to substitute 10 atomic %Cu into Ag at 1000 K, but not 20 atomic %Ag according to Example Problem 4.8. In Chapter 5 we
will see that indeed 20 atomic %copper does not mix into silver at 1000 K (727°C) but 10 atomic %does substitute.
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Motional Emf: It is known that birds can detect the earth's magnetic field, but the mechanism of how they do this is not known. It has been suggested that perhaps they detect a motional emf as they fly north to south, but it turns out that the induced voltages are small compared to the voltages normally encountered in cells, so this is probably not the mechanism involved. To check this out, calculate the induced voltage across the wingtips of a wild goose with a wingspan of 1.2 m if it is flying directly south at 13 m/s at a point where the earth's magnetic field is 5.0 ×10-5 T directed downward from the horizontal by 40?.
A. 0.50 mV B. 0.60 mV C. 0.78 mV D. 0.060 mV E. 0.25 mV
Mass number refers to the number of
A) protons in the nucleus. B) neutrons in the nucleus. C) nucleons in the nucleus.
A non-conducting sphere of radius R = 7.0 cm carries a charge Q = 4.0 mC distributed uniformly throughout its volume. At what distance, measured from the center of the sphere, does the electric field reach a value equal to half its maximum value?
A) 3.5 cm only B) 4.9 cm only C) 3.5 cm and 9.9 cm D) 3.5 cm and 4.9 cm E) 9.9 cm only
What happens in electron capture?
a. The nucleus emits an electron, a neutron becomes a proton, and the atomic number goes up. b. The nucleus absorbs an electron, a proton becomes a neutron, and the atomic number goes down. c. The nucleus emits a positron, a neutron becomes a proton, and the atomic number goes down. d. The nucleus emits an electron, a neutron becomes a proton, and the atomic number goes down. e. The nucleus absorbs an electron, a proton becomes a neutron, and the atomic number goes up.