Chapter 6

The internal energy of a system increased by \(400 \mathrm{~J}\) when it absorbed \(600 \mathrm{~J}\) of heat. (a) Was work done by or on the system? (b) How much work was done?

(a) Describe three ways in which you could increase the internal energy of an open system. (b) Which of these methods could you use to increase the internal energy of a closed system? (c) Which, if any, of these methods could you use to increase the internal energy of an isolated system?

If a \(70-\mathrm{kg}\) male burns \(2000 \mathrm{~kJ}\) of energy while jogging for \(1.0 \mathrm{~h}\), what mass of fat would be consumed, given that the typical standard energy of combustion of fat is about \(38 \mathrm{~kJ} \cdot \mathrm{g}^{-1}\) ? How many hours would he need to jog if he wished to lose \(0.50 \mathrm{~kg}\) of fat?

Strong sunshine bombards the Earth with about \(1 \mathrm{~kJ} \cdot \mathrm{m}^{-2}\) in \(1 \mathrm{~s}\). Calculate the maximum mass of pure ethanol that can be vaporized in 10 min from a beaker left in strong sunshine, assuming the surface area of the ethanol to be \(50 \mathrm{~cm}^{2}\). Assume all the heat is used for vaporization, not to increase the temperature.

When \(25.0 \mathrm{~g}\) of a metal at a temperature of \(90.0^{\circ} \mathrm{C}\) is added to \(50.0 \mathrm{~g}\) of water at \(25.0^{\circ} \mathrm{C}\), the water temperature rises to \(29.8^{\circ} \mathrm{C}\). The specific heat capacity of water is \(4.184 \mathrm{~J}-\left({ }^{\circ} \mathrm{C}\right)^{-1} \mathrm{~g}^{-1}\). What is the specific heat capacity of the metal?

The heat capacity of a certain empty calorimeter is \(488.1 \mathrm{~J} \cdot\left({ }^{\circ} \mathrm{C}\right)^{-1}\). When \(25.0 \mathrm{~mL}\) of \(0.700 \mathrm{M}\) \(\mathrm{NaOH}(\mathrm{aq})\) was mixed in that calorimeter with \(25.0 \mathrm{~mL}\) of \(0.700 \mathrm{M} \mathrm{HCl}\) (aq), both initially at \(20.00^{\circ} \mathrm{C}\), the temperature increased to \(21.34^{\circ} \mathrm{C}\). Calculate the enthalpy of neutralization in kilojoules per mole of HCI.

Calculate the lattice enthalpy of solid potassium bromide, \(\mathrm{KBr}(\mathrm{s}) \rightarrow \mathrm{K}^{+}(\mathrm{g})+\mathrm{Br}^{-}(\mathrm{g})\), from the following information: $$ \begin{aligned} &\Delta H_{i}{ }^{\circ}\left(\mathrm{KBr}, \text { s) }=-394 \mathrm{~kJ} \cdot \mathrm{mol}^{-1}\right. \\ &\Delta H_{i}{ }^{\circ}(\mathrm{K}, \mathrm{g})=+89.2 \mathrm{~kJ} \cdot \mathrm{mol}^{-1} \end{aligned} $$ First ionization energy of \(\mathrm{K}(\mathrm{g})=+425.0 \mathrm{~kJ} \cdot \mathrm{mol}^{-1}\) \(\Delta H_{\text {vap }}{ }^{\circ}\left(\mathrm{Br}_{2}, \mathrm{l}\right)=+30.9 \mathrm{~kJ} \cdot \mathrm{mol}^{-1}\) Br-Br bond dissociation cuthalpy \(=+192.9 \mathrm{~kJ} \cdot \mathrm{mol}^{-1}\) Electron attachment to \(\mathrm{Br}(\mathrm{g})\) : $$ \mathrm{Br}(\mathrm{g})+\mathrm{e}^{-}(\mathrm{g}) \rightarrow \mathrm{Be}^{-}(\mathrm{g}), \quad \Delta H^{*}=-331.0 \mathrm{~kJ} $$