OC userin Chemistry·3 Nov 2017119. A 67.2 g sample of a gold and palladium alloy contains 2.49 X 1023 atoms. What is the composition (by mass) of the alloy?
OC userin Chemistry·31 Oct 2017114. The A — first-order integrated rate law for the reaction products is derived from the rate law using calculus: Rate = k[A] (first-order rate law) d[A] Ratedt [A] =- [A] The equation just given is a first-order, separable differential equation that can be solved by separating the variables and inte- grating: d[A] = -kdt TAJ PINA[A] - kat JA), [A] kat In the integral just given, [A]o is the initial concentration of A. We then evaluate the integral: [In[A]] A) = -k[t]6 In[A] - In[A]o = -kt In[A] = -kt + In[A]o (integrated rate law) a. Use a procedure similar to the one just shown to derive an in- tegrated rate law for a reaction A — products, which is one- half order in the concentration of A (that is, Rate = k[A]"). b. Use the result from part a to derive an expression for the half- life of a one-half-order reaction.
OC userin Chemistry·1 Nov 2017100. Silver can be electroplated at the cathode of an electrolysis cell by the half-reaction: Ag+ (aq) + Ag(s) What mass of silver would plate onto the cathode if a current of 6.8 A flowed through the cell for 72 min?
OC userin Chemistry·31 Oct 201780. Consider the reaction: 2 NO(g) + O2(g) = 2 NO2(8) The following data show the equilibrium constant for this reac- tion measured at several different temperatures. Use the data to find A Hexn and ASixn for the reaction. Temperature 170 K. 3.8 x 10-3 180 K 0.34 190 K 18.4 200 K 681
OC userin Chemistry·1 Nov 2017105. Consider the unbalanced redox reaction: MnO4 (aq) + Zn(s) — Mn2+ (aq) + Zn2+ (aq) Balance the equation and determine the volume of a 0.500 M KMnO4 solution required to completely react with 2.85 g of Zn.
OC userin Chemistry·30 Oct 2017Q6. The Zn/Zn²+ electrode has a standard electrode potential of E = -0.76 V. How does the relative potential energy of an electron at the Zn/Zn2+ electrode compare to the potential energy of an electron at the standard hydrogen electrode? a) An electron at the Zn/Zn2+ electrode has a higher potential energy than an electron at the standard hydrogen electrode. b) An electron at the Zn/Zn2+ electrode has a lower potential energy than an electron at the standard hydrogen electrode. c) An electron at the Zn/Zn2+ electrode has the same potential energy as an electron at the standard hydrogen electrode. d) Nothing can be concluded about the relative potential energy of an electron at the standard electrode potential.
OC userin Chemistry·30 Oct 201738. Sulfur and fluorine form several different compounds including sulfur hexafluoride and sulfur tetrafluoride. Decomposition of a sample of sulfur hexafluoride produces 4.45 g of fluorine and 1.25 g of sulfur, while decomposition of a sample of sulfur tetra- fluoride produces 4.43 g of fluorine and 1.87 g of sulfur. Calcu- late the mass of fluorine per gram of sulfur for each sample and show that these results are consistent with the law of multiple proportions.
OC userin Chemistry·30 Oct 201787. Ethene (C2H4) can be halogenated by the reaction: C2H4(8) + X2(g) = C2H4X2(8) where X2 can be Cl2, Br2, or 12. Use the thermodynamic data given to calculate AH, AS, AG®, and K, for the halogenation reaction by each of the three halogens at 25°C. Which reaction is most spontaneous? Least spontaneous? What is the main fac- tor responsible for the difference in the spontaneity of the three reactions? Does higher temperature make the reactions more spontaneous or less spontaneous? Compound AH; (kJ/mol) Sº (J/mol ·K) 308.0 C2H4Cl2(g) -129.7 +38.3 C2H4Br2(g) C2H412(g) 330.6 347.8 +66.5
OC userin Chemistry·30 Oct 201773. Ultraviolet radiation and radiation of shorter wavelengths can damage biological molecules because these kinds of radiation carry enough energy to break bonds within the molecules. A typical carbon-carbon bond requires 348 kJ/mol to break. What is the longest wavelength of radiation with enough ener gy to break carbon-carbon bonds?
OC userin Chemistry·30 Oct 201756. The fluids within cells are buffered by H2PO4 and HPO42- a. Calculate the ratio of HPO42-to H2PO4 required to main- tain a pH of 7.1 within a cell. b. Could a buffer system employing H3PO4 as the weak acid and H2PO4 as the weak base be used as a buffer system within cells? Explain.
OC userin Chemistry·29 Oct 201743. A laser pulse with wavelength 532 nm contains 3.85 m) of energy. How many photons are in the laser pulse?
OC userin Chemistry·29 Oct 20177. How and by whom was the electron discovered? What basic properties of the electron were reported with its discovery?
OC userin Chemistry·29 Oct 2017113. In this chapter we have seen a number of reactions in which a single reactant forms products. For example, consider the fol lowing first-order reaction: CH3NC(g) -CH,CN(g) However, we also learned that gas-phase reactions occur through collisions. a. One possible explanation for how this reaction occurs is that two molecules of CH3NC collide with each other and form two molecules of the product in a single elementary step. If that were the case, what reaction order would you expect? b. Another possibility is that the reaction occurs through more than one step. For example, a possible mechanism involves one step in which the two CH3NC molecules collide, result- ing in the "activation" of one of them. In a second step, the activated molecule goes on to form the product. Write down this mechanism and determine which step must be rate determining in order for the kinetics of the reaction to be first order. Show explicitly how the mechanism predicts first order kinetics.
OC userin Chemistry·26 Oct 201781. A concentration cell consists of two Sn/Sn2+ half-cells. The cell has a potential of 0.10 V at 25°C. What is the ratio of the Sn2+ concentrations in the two half-cells?