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Chapter 5: Problem 31
During a deep breath, our lungs expand about \(2.0 \mathrm{~L}\) against an external pressure of \(101.3 \mathrm{kPa}\). How much work is involved in this process (in J)?
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A magnesium ion, \(\mathrm{Mg}^{2+}\), with a charge of $3.2 \times 10^{-19} \mathrm{C}\( and an oxide ion, \)\mathrm{O}^{2-},\( with a charge of \)-3.2 \times 10^{-19} \mathrm{C},\( are separated by a distance of \)0.35 \mathrm{nm}$. How much work would be required to increase the separation of the two ions to an infinite distance?
Consider the following reaction: $$ 2 \mathrm{Mg}(s)+\mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{MgO}(s) \quad \Delta H=-1204 \mathrm{~kJ} $$ (a) Is this reaction exothermic or endothermic? (b) Calculate the amount of heat transferred when \(3.55 \mathrm{~g}\) of \(\mathrm{Mg}(s)\) reacts at constant pressure. (c) How many grams of \(\mathrm{MgO}\) are produced during an enthalpy change of \(-234 \mathrm{~kJ}\) ? (d) How many kilojoules of heat are absorbed when \(40.3 \mathrm{~g}\) of \(\mathrm{MgO}(s)\) is decomposed into \(\mathrm{Mg}(s)\) and \(\mathrm{O}_{2}(g)\) at constant pressure?
(a) According to the first law of thermodynamics, what quantity is conserved? (b) What is meant by the internal energy of a system? (c) By what means can the internal energy of a closed system increase?
The decomposition of sodium bicarbonate (baking soda), \(\mathrm{NaHCO}_{3}(s)\), into $\mathrm{Na}_{2} \mathrm{CO}_{3}(s), \mathrm{H}_{2} \mathrm{O}(l)\(, and \)\mathrm{CO}_{2}(g)$ at constant pressure requires the addition of \(85 \mathrm{~kJ}\) of heat per two moles of \(\mathrm{NaHCO}_{3} .\) (a) Write a balanced thermochemical equation for the reaction. (b) Draw an enthalpy diagram for the reaction.
When an 18.6-g sample of solid potassium hydroxide dissolves in $200.0 \mathrm{~g}$ of water in a coffee-cup calorimeter (Figure 5.18), the temperature rises from 23.7 to \(44.5^{\circ} \mathrm{C}\). (a) Calculate the quantity of heat (in kJ) released in the reaction. (b) Using your result from part (a), calculate \(\Delta H\) (in kJ/mol KOH) for the solution process. Assume that the specific heat of the solution is the same as that of pure water.
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