Chemistry Textbooks (139)

In a constant-pressure calorimetry experiment, a \(2.675-\mathrm{g}\) piece of zinc metal is dropped into \(100.0 \mathrm{~mL}\) of \(1.75 \mathrm{M}\) hydrochloric acid in a closed vessel with a movable piston. The pressure and temperature in the laboratory are 769 torr and \(23.8^{\circ}\), respectively. Calculate the work done by the system.

A redox reaction employed in an electrochemical cell has a negative \(\Delta G_{\mathrm{rxn}}^{\circ} .\) Which statement is true? a. \(E_{\text {cell }}^{\circ}\) is positive; \(K<1\) b. \(E_{\text {cell }}^{\circ}\) is positive; \(K>1\) c. \(E_{\text {cell }}^{\circ}\) is negative; \(K>1\) d. \(E_{\text {cell }}^{\circ}\) is negative; \(K<1\)

Calculate number of neutrons present in \(12 \times 10^{25}\) atoms of oxygen \(\left({ }_{8} \mathrm{O}^{17}\right):\) (Given: \(\left.N_{A}=6 \times 10^{23}\right)\) (a) 1800 (b) 1600 (c) \(1800 \mathrm{~N}_{\mathrm{A}}\) (d) \(3200 \mathrm{~N}_{A}\)

(i) Given that the cell parameter for calcium oxide, which crystallizes with the sodium chloride structure, is \(483 \mathrm{pm}\), calculate the lattice energy for \(\mathrm{CaO}\). (ii) Using the following data and the lattice energy calculated in part (i), construct a thermochemical cycle for the formation of calcium oxide from its elements and hence calculate the enthalpy of formation of \(\mathrm{CaO}_{(\mathrm{s})}\) : \(\Delta H_{\text {sub }}=+177 ;\) ionization potentials: first \(=+590 ;\) second \(=\) \(+1100 ; \Delta H_{\text {diss }}=+498 ;\) first \(E_{\mathrm{a}}=142 ;\) second \(E_{\mathrm{a}}=-844\left(\mathrm{~kJ} \mathrm{~mol}^{-1}\right)\) (iii) Why might you expect the answer calculated in (ii) to have an error of about \(5 \mathrm{~kJ} \mathrm{~mol}^{-1 ?}\) (iv) Why is the second ionization potential for calcium much greater than the first despite forming a stable closed-shell configuration?

Product Concentrations A \(10^{-3} \mathrm{M}\) solution of gamma globulin (antibodies) is called a "concentrated solution." Why is it called a concentrated solution? Support your answer with a calculation.