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Chapter 7: 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. Solid KBr dissolved in water

In this process, the solution gets colder when solid KBr (potassium bromide) is dissolved in water. This indicates that heat is being absorbed from the surroundings (which is why the temperature of the solution decreases). Therefore, this process is endothermic.
02

b. Natural gas burned in a furnace

When natural gas (CH4 or methane) is burned in a furnace, a combustion reaction takes place. Combustion reactions are exothermic processes, as they release heat to the surroundings. Therefore, this process (burning natural gas) is exothermic.
03

c. Concentrated H2SO4 added to water

When concentrated sulfuric acid (H2SO4) is added to water, the solution gets very hot as a result of the heat generated from the reaction. Since the temperature of the solution increases because heat is released, this process is exothermic.
04

d. Water boiled in a teakettle

Boiling water in a teakettle requires heat in order to change the state of water from liquid to vapor. This process absorbs heat from its surroundings, making it an endothermic process.

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Most popular questions from this chapter

The bomb calorimeter in Exercise 102 is filled with 987 g water. The initial temperature of the calorimeter contents is \(23.32^{\circ} \mathrm{C} . \mathrm{A}\) \(1.056-\mathrm{g}\) sample of benzoic acid \(\left(\Delta E_{\text {comb }}=-26.42 \mathrm{kJ} / \mathrm{g}\right)\) is combusted in the calorimeter. What is the final temperature of the calorimeter contents?

The enthalpy of combustion of \(\mathrm{CH}_{4}(g)\) when \(\mathrm{H}_{2} \mathrm{O}(l)\) is formed is \(-891 \mathrm{kJ} / \mathrm{mol}\) and the enthalpy of combustion of \(\mathrm{CH}_{4}(g)\) when \(\mathrm{H}_{2} \mathrm{O}(g)\) is formed is \(-803 \mathrm{kJ} / \mathrm{mol} .\) Use these data and Hess's law to determine the enthalpy of vaporization for water.

One mole of \(\mathrm{H}_{2} \mathrm{O}(g)\) at 1.00 atm and \(100 .^{\circ} \mathrm{C}\) occupies a volume of 30.6 L. When 1 mole of \(\mathrm{H}_{2} \mathrm{O}(g)\) is condensed to 1 mole of \(\mathrm{H}_{2} \mathrm{O}(l)\) at 1.00 atm and \(100 .^{\circ} \mathrm{C}, 40.66 \mathrm{kJ}\) of heat is released. If the density of \(\mathrm{H}_{2} \mathrm{O}(l)\) at this temperature and pressure is \(0.996 \mathrm{g} / \mathrm{cm}^{3},\) calculate \(\Delta E\) for the condensation of 1 mole of water at 1.00 atm and \(100 .^{\circ} \mathrm{C}\).

The standard enthalpy of combustion of ethene gas, \(\mathrm{C}_{2} \mathrm{H}_{4}(g)\) is \(-1411.1 \mathrm{kJ} / \mathrm{mol}\) at \(298 \mathrm{K}\). Given the following enthalpies of formation, calculate \(\Delta H_{\mathrm{f}}^{\circ}\) for \(\mathrm{C}_{2} \mathrm{H}_{4}(g)\). $$\begin{array}{ll}\mathrm{CO}_{2}(g) & -393.5 \mathrm{kJ} / \mathrm{mol} \\\\\mathrm{H}_{2} \mathrm{O}(l) & -285.8 \mathrm{kJ} / \mathrm{mol}\end{array}$$

What is meant by the term lower in energy? Which is lower in energy, a mixture of hydrogen and oxygen gases or liquid water? How do you know? Which of the two is more stable? How do you know?
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