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Chapter 6: Problem 43

Are the following processes exothermic or endothermic? a. When solid \(\mathrm{KBr}\) is dissolved in water, the solution gets colder. b. Natural gas \(\left(\mathrm{CH}_{4}\right)\) is burned in a furnace. c. When concentrated \(\mathrm{H}_{2} \mathrm{SO}_{4}\) is added to water, the solution gets very hot. d. Water is boiled in a teakettle.

Short Answer

Expert verified
a. Endothermic b. Exothermic c. Exothermic d. Endothermic

Step by step solution

01

a. Dissolving \(\mathrm{KBr}\) in Water

The statement says that when solid \(\mathrm{KBr}\) is dissolved in water, the solution gets colder. This indicates that heat is being absorbed by the solution from the surroundings. Since heat is being absorbed, this process is endothermic.
02

b. Burning Natural Gas (\(\mathrm{CH}_{4}\))

Burning natural gas (\(\mathrm{CH}_{4}\)) in a furnace is a combustion reaction. Combustion reactions are typically exothermic, as they release heat to the surroundings. Therefore, this process is exothermic.
03

c. Adding Concentrated \(\mathrm{H}_{2}\mathrm{SO}_{4}\) to Water

When concentrated \(\mathrm{H}_{2}\mathrm{SO}_{4}\) is added to water, the solution gets very hot. This means that heat is being released by the solution to the surroundings. Since heat is being released, this process is exothermic.
04

d. Boiling Water in a Teakettle

Boiling water in a teakettle requires heat to be absorbed from the surroundings (i.e., from the heat source) to break the hydrogen bonds and initiate phase transition from liquid to gas. Since heat is being absorbed, this process is endothermic. In summary: a. Dissolving \(\mathrm{KBr}\) in water: Endothermic b. Burning natural gas (\(\mathrm{CH}_{4}\)): Exothermic c. Adding concentrated \(\mathrm{H}_{2}\mathrm{SO}_{4}\) to water: Exothermic d. Boiling water in a teakettle: Endothermic

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Most popular questions from this chapter

The enthalpy of combustion of solid carbon to form carbon dioxide is \(-393.7 \mathrm{~kJ} / \mathrm{mol}\) carbon, and the enthalpy of combustion of carbon monoxide to form carbon dioxide is \(-283.3 \mathrm{~kJ} /\) mol CO. Use these data to calculate \(\Delta H\) for the reaction $$ 2 \mathrm{C}(s)+\mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{CO}(g) $$

Assume that \(4.19 \times 10^{6} \mathrm{~kJ}\) of energy is needed to heat a home. If this energy is derived from the combustion of methane \(\left(\mathrm{CH}_{4}\right)\), what volume of methane, measured at STP, must be burned? \(\left(\Delta H_{\text {combustion }}^{\circ}\right.\) for \(\mathrm{CH}_{4}=-891 \mathrm{~kJ} / \mathrm{mol}\) )

Given the following data $$ \begin{aligned} \mathrm{P}_{4}(s)+6 \mathrm{Cl}_{2}(g) & \longrightarrow 4 \mathrm{PCl}_{3}(g) & & \Delta H=-1225.6 \mathrm{~kJ} \\ \mathrm{P}_{4}(s)+5 \mathrm{O}_{2}(g) & \longrightarrow \mathrm{P}_{4} \mathrm{O}_{10}(s) & & \Delta H=-2967.3 \mathrm{~kJ} \\ \mathrm{PCl}_{3}(g)+\mathrm{Cl}_{2}(g) \longrightarrow \mathrm{PCl}_{5}(g) & & \Delta H=-84.2 \mathrm{~kJ} \\ \mathrm{PCl}_{3}(g)+\frac{1}{2} \mathrm{O}_{2}(g) \longrightarrow \mathrm{Cl}_{3} \mathrm{PO}(g) & & \Delta H=-285.7 \mathrm{~kJ} \end{aligned} $$ calculate \(\Delta H\) for the reaction $$ \mathrm{P}_{4} \mathrm{O}_{10}(s)+6 \mathrm{PCl}_{5}(g) \longrightarrow 10 \mathrm{Cl}_{3} \mathrm{PO}(g) $$

Hydrogen gives off \(120 . \mathrm{J} / \mathrm{g}\) of energy when burned in oxygen, and methane gives off \(50 . \mathrm{J} / \mathrm{g}\) under the same circumstances. If a mixture of \(5.0 \mathrm{~g}\) hydrogen and \(10 . \mathrm{g}\) methane is burned, and the heat released is transferred to \(50.0 \mathrm{~g}\) water at \(25.0^{\circ} \mathrm{C}\), what final temperature will be reached by the water?

Consider the following reaction: $$ 2 \mathrm{H}_{2}(g)+\mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{H}_{2} \mathrm{O}(l) \quad \Delta H=-572 \mathrm{~kJ} $$ a. How much heat is evolved for the production of \(1.00 \mathrm{~mole}\) of \(\mathrm{H}_{2} \mathrm{O}(l)\) ? b. How much heat is evolved when \(4.03 \mathrm{~g}\) hydrogen are reacted with excess oxygen? c. How much heat is evolved when \(186 \mathrm{~g}\) oxygen are reacted with excess hydrogen? d. The total volume of hydrogen gas needed to fill the Hindenburg was \(2.0 \times 10^{8} \mathrm{~L}\) at \(1.0\) atm and \(25^{\circ} \mathrm{C}\). How much heat was evolved when the Hindenburg exploded, assuming all of the hydrogen reacted?
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