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Chapter 6: Problem 7

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

Short Answer

Expert verified
Thermochemistry is the study of heat energy associated with chemical reactions. An exothermic process is one that releases heat into its surroundings, while an endothermic process absorbs heat from its surroundings.

Step by step solution

01

Definition of Thermochemistry

The term 'thermochemistry' originates from two words, 'thermo' referring to heat and 'chemistry'. Thermochemistry is the study of the heat energy associated with chemical reactions and/or physical transformations. It includes the concepts of enthalpy, entropy, Gibbs free energy, and more.
02

Definition of Exothermic Process

An exothermic process refers to a reaction or process that releases heat into its surroundings. The energy needed for the reaction to occur is less than the total energy released. Examples of exothermic processes include combustion reactions, neutralization reactions, or even the process of freezing.
03

Definition of Endothermic Process

An endothermic process, in contrast, absorbs heat from its surroundings. The energy needed for the reaction to occur is more than the total energy released. This process results in a decrease in temperature in its surroundings. Examples include the process of melting ice or the process of photosynthesis in plants.

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Most popular questions from this chapter

Which of the following standard enthalpy of formation values is not zero at \(25^{\circ} \mathrm{C} ? \mathrm{Na}(s), \mathrm{Ne}(g)\) \(\mathrm{CH}_{4}(g), \mathrm{S}_{8}(s), \mathrm{Hg}(l), \mathrm{H}(g)\)

What is heat? How does heat differ from thermal energy? Under what condition is heat transferred from one system to another?

Consider two metals A and B, each having a mass of \(100 \mathrm{~g}\) and an initial temperature of \(20^{\circ} \mathrm{C}\). The specific heat of \(A\) is larger than that of \(B\). Under the same heating conditions, which metal would take longer to reach a temperature of \(21^{\circ} \mathrm{C} ?\)

Lime is a term that includes calcium oxide \((\mathrm{CaO}\) also called quicklime) and calcium hydroxide \(\left[\mathrm{Ca}(\mathrm{OH})_{2},\right.\) also called slaked lime \(] .\) It is used in the steel industry to remove acidic impurities, in airpollution control to remove acidic oxides such as \(\mathrm{SO}_{2}\), and in water treatment. Quicklime is made industrially by heating limestone \(\left(\mathrm{CaCO}_{3}\right)\) above \(2000^{\circ} \mathrm{C}\) : $$ \begin{aligned} \mathrm{CaCO}_{3}(s) \longrightarrow \mathrm{CaO}(s)+\mathrm{CO}_{2}(g) \\ \Delta H^{\circ} &=177.8 \mathrm{~kJ} / \mathrm{mol} \end{aligned} $$ Slaked lime is produced by treating quicklime with water: $$ \begin{aligned} \mathrm{CaO}(s)+\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow \mathrm{Ca}(\mathrm{OH})_{2}(s) \\ \Delta H^{\circ} &=-65.2 \mathrm{~kJ} / \mathrm{mol} \end{aligned} $$ The exothermic reaction of quicklime with water and the rather small specific heats of both quicklime \(\left(0.946 \mathrm{~J} / \mathrm{g} \cdot{ }^{\circ} \mathrm{C}\right)\) and slaked lime \(\left(1.20 \mathrm{~J} / \mathrm{g} \cdot{ }^{\circ} \mathrm{C}\right)\) make it hazardous to store and transport lime in vessels made of wood. Wooden sailing ships carrying lime would occasionally catch fire when water leaked into the hold. (a) If a 500 -g sample of water reacts with an equimolar amount of \(\mathrm{CaO}\) (both at an initial temperature of \(\left.25^{\circ} \mathrm{C}\right)\), what is the final temperature of the product, \(\mathrm{Ca}(\mathrm{OH})_{2} ?\) Assume that the product absorbs all of the heat released in the reaction. (b) Given that the standard enthalpies of formation of \(\mathrm{CaO}\) and \(\mathrm{H}_{2} \mathrm{O}\) are \(-635.6 \mathrm{~kJ} / \mathrm{mol}\) and \(-285.8 \mathrm{~kJ} / \mathrm{mol}\), respectively, cal- culate the standard enthalpy of formation of \(\mathrm{Ca}(\mathrm{OH})_{2}\).

The combustion of \(0.4196 \mathrm{~g}\) of a hydrocarbon releases \(17.55 \mathrm{~kJ}\) of heat. The masses of the products are \(\mathrm{CO}_{2}=1.419 \mathrm{~g}\) and \(\mathrm{H}_{2} \mathrm{O}=0.290 \mathrm{~g} .\) (a) What is the empirical formula of the compound? (b) If the approximate molar mass of the compound is \(76 \mathrm{~g}\), calculate its standard enthalpy of formation.
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