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Chapter 7: Problem 116

Which of the following processes are exothermic? a. \(\mathrm{N}_{2}(g) \longrightarrow 2 \mathrm{N}(g)\) b. \(\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow \mathrm{H}_{2} \mathrm{O}(s)\) c. \(\mathrm{Cl}_{2}(g) \longrightarrow 2 \mathrm{Cl}(g)\) d. \(2 \mathrm{H}_{2}(g)+\mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{H}_{2} \mathrm{O}(g)\) e. \(\mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{O}(g)\)

Short Answer

Expert verified
The exothermic processes among the given options are b. \(H_2O(l) \longrightarrow H_2O(s)\) and d. \(2 H_2(g) + O_2(g) \longrightarrow 2 H_2O(g)\).

Step by step solution

01

a. N2(g) → 2 N(g)

In this process, we are breaking the triple bond between two nitrogen atoms in the nitrogen molecule to form two separate nitrogen atoms. Breaking a bond requires energy, so this process is endothermic, not exothermic.
02

b. H2O(l) → H2O(s)

In this process, liquid water is being converted to solid water (ice). As water freezes, it forms a lattice structure that leads to the formation of hydrogen bonds. The creation of hydrogen bonds releases energy, making this process exothermic.
03

c. Cl2(g) → 2 Cl(g)

In this process, we are breaking the single bond between two chlorine atoms in the chlorine molecule to form two separate chlorine atoms. Breaking a bond requires energy, so this process is endothermic, not exothermic.
04

d. 2 H2(g) + O2(g) → 2 H2O(g)

In this process, hydrogen and oxygen molecules are reacting to form water molecules. During this reaction, the bonds in the hydrogen and oxygen molecules are broken and new bonds are formed in the water molecules. The overall energy released in forming new bonds is more than the energy required to break the initial bonds, making this process exothermic.
05

e. O2(g) → 2 O(g)

In this process, we are breaking the double bond between two oxygen atoms in the oxygen molecule to form two separate oxygen atoms. Breaking a bond requires energy, so this process is endothermic, not exothermic. In conclusion, processes b and d are exothermic, while processes a, c, and e are endothermic.

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Most popular questions from this chapter

Give the definition of the standard enthalpy of formation for a substance. Write separate reactions for the formation of NaCl, \(\mathrm{H}_{2} \mathrm{O}, \mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6},\) and \(\mathrm{PbSO}_{4}\) that have \(\Delta H^{\circ}\) values equal to \(\Delta H_{\mathrm{f}}^{\circ}\) for each compound.

Consider a mixture of air and gasoline vapor in a cylinder with a piston. The original volume is \(40 . \mathrm{cm}^{3} .\) If the combustion of this mixture releases \(950 .\) \(\mathrm{J}\) of energy, to what volume will the gases expand against a constant pressure of \(650 .\) torr if all the energy of combustion is converted into work to push back the piston?

Consider the following cyclic process carried out in two steps on a gas: Step \(1: 45 \mathrm{J}\) of heat is added to the gas, and \(10 . \mathrm{J}\) of expansion work is performed. Step \(2: 60. \mathrm{J}\) of heat is removed from the gas as the gas is compressed back to the initial state. Calculate the work for the gas compression in Step 2.

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.

Consider the following reaction: $$\mathrm{CH}_{4}(g)+2 \mathrm{O}_{2}(g) \longrightarrow \mathrm{CO}_{2}(g)+2 \mathrm{H}_{2} \mathrm{O}(l) \quad \Delta H=-891 \mathrm{kJ}$$ Calculate the enthalpy change for each of the following cases: a. \(1.00 \mathrm{g}\) methane is burned in excess oxygen. b. \(1.00 \times 10^{3} \mathrm{L}\) methane gas at \(740 .\) torr and \(25^{\circ} \mathrm{C}\) are burned in excess oxygen. The density of \(\mathrm{CH}_{4}(g)\) at these conditions is \(0.639 \mathrm{g} / \mathrm{L}\).
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