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Chapter 6: Problem 101

Decomposition reactions are usually endothermic, whereas combination reactions are usually exothermic. Give a qualitative explanation for these trends.

Short Answer

Expert verified
Decomposition reactions are endothermic because they require energy to break the existing chemical bonds in the compound. On the other hand, combination reactions are exothermic because they release energy when the new chemical bonds are formed.

Step by step solution

01

Understanding Decomposition Reactions

In a decomposition reaction, a single compound breaks down into two or more simpler substances. This reaction requires heat (energy) to break the chemical bonds in the compound. Therefore, decomposition reactions are usually endothermic - they absorb heat from the surroundings.
02

Understanding Combination Reactions

In a combination reaction, two or more substances combine to form a more complex substance. When substances combine, the chemical bonds between atoms are formed. The formation of bonds releases energy, hence combination reactions are usually exothermic - they release heat to the surroundings.
03

Correlation Between Reaction Type and Energy Transfer

The trends observed (endothermic decomposition reactions and exothermic combination reactions) can be attributed to the nature of chemical bonds. Breaking bonds (as in decomposition) requires energy input (endothermic), while forming bonds (as in combination) releases energy (exothermic).

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Most popular questions from this chapter

Consider these changes. (a) \(\operatorname{Hg}(l) \longrightarrow \operatorname{Hg}(g)\) (b) \(3 \mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{O}_{3}(g)\) (c) \(\mathrm{CuSO}_{4} \cdot 5 \mathrm{H}_{2} \mathrm{O}(s) \longrightarrow \mathrm{CuSO}_{4}(s)+5 \mathrm{H}_{2} \mathrm{O}(g)\) (d) \(\mathrm{H}_{2}(g)+\mathrm{F}_{2}(g) \longrightarrow 2 \mathrm{HF}(g)\) At constant pressure, in which of the reactions is work done by the system on the surroundings? By the surroundings on the system? In which of them is no work done?

Define these terms: thermochemistry, exothermic process, endothermic process.

A quantity of 0.020 mole of a gas initially at \(0.050 \mathrm{~L}\) and \(20^{\circ} \mathrm{C}\) undergoes a constant-temperature expansion until its volume is \(0.50 \mathrm{~L}\). Calculate the work done (in joules) by the gas if it expands (a) against a vacuum and (b) against a constant pressure of 0.20 atm. (c) If the gas in (b) is allowed to expand unchecked until its pressure is equal to the external pressure, what would its final volume be before it stopped expanding, and what would be the work done?

What is meant by the standard-state condition?

(a) For most efficient use, refrigerator freezer compartments should be fully packed with food. What is the thermochemical basis for this recommendation? (b) Starting at the same temperature, tea and coffee remain hot longer in a thermal flask than chicken noodle soup. Explain.
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