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Thermochemistry

In thermochemistry, thermochemistry or thermochmistry is the branch of chemistry concerned with the chemical reactions of chemical substances at high temperatures. In general, thermochemistry involves the study of chemical changes at high temperatures. In contrast to ordinary chemistry, which is concerned with molecular processes at room temperature, thermochemistry studies reactions that take place at temperatures significantly higher than room temperature or in the presence of a large amount of heat energy. The field of thermochemistry was founded by the Prussian chemist Hermann Kolbe in 1857. The term "thermochemistry" was coined by the German chemist Ludwig Mond in 1864. In 1847, the French chemist Marcellin Berthelot (1827-1907) discovered that the heat of combustion of organic compounds is independent of the specific chemical compound. He noted that the heat of combustion of a number of hydrocarbons (e.g., benzene, toluene, ethylene) was the same. The German chemist Fritz Haber (1868-1934) showed that the heat of combustion of aldehydes is also independent of the type of aldehyde. Haber studied the heat of combustion of a series of aldehydes and ketones, and the results were the same for many of the compounds. However, the heat of combustion of acrolein (a product of the thermal decomposition of acrolein) was found to vary with the specific chemical structure of the aldehyde or ketone. This observation was due to the fact that the reaction between acrolein and an aldehyde or ketone forms a hemiacetal or hemiketal intermediate. In 1885, the French chemist Marcellin Berthelot (1827-1907) was the first to note the influence of temperature on the heat of combustion of organic compounds. He showed that the heat of combustion of a number of hydrocarbons (e.g., benzene, toluene, ethylene) was the same. He also noted that the heat of combustion of aldehydes was independent of the aldehyde's structure. The German chemist Fritz Haber (1868-1934) showed that the heat of combustion of aldehydes was also independent of the type of aldehyde. Haber studied the heat of combustion of a series of aldehydes and ketones, and the results were the same for many of the compounds. However, the heat of combustion of acrolein (a product of the thermal decomposition of acrolein) was found to vary with the specific chemical structure of the aldehyde or ketone. This observation was due to the fact that the reaction between acrolein and an aldehyde or ketone forms a hemiacetal or hemiketal intermediate. In 1887, the German chemist Hermann Kolbe (1837-1912) published a comprehensive survey of all reactions known to occur between organic compounds and heat. The work was the first comprehensive study of heat reactions in organic chemistry to appear in a language other than German. It is also the first book to include reactions between organic compounds and heat. In the following year, Kolbe published a second volume covering reactions involving the elements. In 1907, he published a third volume, which covered reactions between organic compounds and the elements. The French chemist Marcellin Berthelot (1827-1907) was the first to note the influence of temperature on the heat of combustion of organic compounds in 1847. He showed that the heat of combustion of a number of hydrocarbons (e.g., benzene, toluene, ethylene) was the same, a finding that was later confirmed by other investigators. He also noted that the heat of combustion of aldehydes was independent of the aldehyde's structure. The German chemist Fritz Haber (1868-1934) showed that the heat of combustion of aldehydes was also independent of the type of aldehyde. Haber studied the heat of combustion of a series of aldehydes and ketones, and the results were the same for many of the compounds. However, the heat of combustion of acrolein (a product of the thermal decomposition of acrolein) was found to vary with the specific chemical structure of the aldehyde or ketone. This observation was due to the fact that the reaction between acrolein and an aldehyde or ketone forms a hemiacetal or hemiketal intermediate. In 1887, the German chemist Hermann Kolbe (1837-1912) published a comprehensive survey of all reactions known to occur between organic compounds and heat. The work was the first comprehensive study of heat reactions in organic chemistry to appear in a language other

Energy

114 Practice Problems
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02:47
Chemistry: Introducing Inorganic, Organic and Physical Chemistry

A student used a calorimeter containing $100 \mathrm{g}$ of deionized water which required an energy change of $818 \mathrm{J}$ to cause a temperature change of $1 \mathrm{K}$
An unknown mass of sodium hydroxide, NaOH, was dissolved in the water and the temperature rose from $25.00^{\circ} \mathrm{C}$ to $31.00^{\circ} \mathrm{C}$. Given that the molar enthalpy of solution of NaOH is $-44.51 \mathrm{kJ} \mathrm{mol}^{-1}$, what mass of sodium hydroxide was dissolved? (Section 13.6)

Energy and thermochemistry
Lottie Adams
00:57
Thermodynamics : An Engineering Approach

Does a refrigerator that has a higher COP necessarily have a higher second-law efficiency than one with a lower COP? Explain.

Energy
Mitchell Cutler
01:30
Thermodynamics : An Engineering Approach

Does a power plant that has a higher thermal efficiency necessarily have a higher second-law efficiency than one with a lower thermal efficiency? Explain.

Energy
Mitchell Cutler

1st Law of Thermodynamics

65 Practice Problems
View More
03:00
Physical Chemistry

The surface tension of water is $71.97 \times 10^{-3} \mathrm{Nm}^{-1}$ or $71.97 \times 10^{-3} \mathrm{Jm}^{-2}$ at $25^{\circ} \mathrm{C}$. Calculate the surface energy in joules of 1 mol of water dispersed as a mist containing droplets of $1 \mu \mathrm{m}\left(10^{-4} \mathrm{cm}\right)$ in radius. The density of water may be taken as $1.00 \mathrm{g} \mathrm{cm}^{-3}$.

First Law of Thermodynamics
Lottie Adams
02:57
Physical Chemistry

One gram of liquid benzene is burned in a bomb calorimeter. The temperature before ignition was $20.826^{\circ} \mathrm{C}$ and the temperature after the combustion was $25.000^{\circ} \mathrm{C}$. This was an adiabatic calorimeter. The heat capacity of the bomb, the water around it, and the contents of the bomb before the combustion was $10000 \mathrm{JK}^{-1}$. Calculate $\Delta_{\mathrm{f}} H^{\circ}$ for $\mathrm{C}_{6} \mathrm{H}_{6}(\mathrm{l})$ at $298.15 \mathrm{K}$ from these data. Assume that the water produced in the combustion is in the liquid state and the carbon dioxide produced in the combustion is in the gas state.

First Law of Thermodynamics
Lottie Adams
02:29
Physical Chemistry

What is the heat evolved in freezing water at $-10^{\circ} \mathrm{Cgiven}$ that
$$\begin{aligned}
\mathrm{H}_{2} \mathrm{O}(\mathrm{l}) &=\mathrm{H}_{2} \mathrm{O}(\mathrm{s}) \quad \Delta H^{\circ}(273 \mathrm{K})=-6004 \mathrm{J} \mathrm{mol}^{-1} \\
\bar{C}_{P}\left(\mathrm{H}_{2} \mathrm{O}, \mathrm{l}\right) &=75.3 \mathrm{J} \mathrm{K}^{-1} \mathrm{mol}^{-1} \\
\bar{C}_{P}\left(\mathrm{H}_{2} \mathrm{O}, \mathrm{s}\right) &=36.8 \mathrm{J} \mathrm{K}^{-1} \mathrm{mol}^{-1}
\end{aligned}$$

First Law of Thermodynamics
Lottie Adams

Enthalpy

138 Practice Problems
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02:37
Chemistry: Introducing Inorganic, Organic and Physical Chemistry

$50.0 \mathrm{cm}^{3}$ of $\mathrm{HCl}$ (aq) of concentration $1.0 \mathrm{moldm}^{-3}$ were mixed with $50.0 \mathrm{cm}^{3}$ of NaOH (aq) of concentration $1.0 \mathrm{moldm}^{-3}$ at $25^{\circ} \mathrm{C}$ in a constant pressure solution calorimeter. After the reactants were mixed the temperature increased to $31.8^{\circ} \mathrm{C}$. Assuming that the solutions have the same density and specific heat capacity as water, calculato the enthalpy change for the neutralization reaction.

Energy and thermochemistry
Lottie Adams
01:08
Chemistry: Introducing Inorganic, Organic and Physical Chemistry

For a reaction at constant pressure, the enthalpy change is $+30 \mathrm{kJ} .$ During the reaction, the system expands and does $25 \mathrm{kJ}$ of work. What is the change in internal energy for the reaction? (Section 13.5 )

Energy and thermochemistry
Lottie Adams
04:34
Chemistry: Introducing Inorganic, Organic and Physical Chemistry

Calculate the enthalpy change when gaseous benzene $\left(\mathrm{C}_{6} \mathrm{H}_{6}\right)$ dissociates into gaseous atoms at $298 \mathrm{K}$. Carry out the calculation by two different methods using the data in (a) and
(b) below. Comment on the difference in the values you obtain
by the two methods. (Section 13.3 )
(a) Assume benzene molecules contain three single and three double carbon-carbon bonds, and use mean bond enthalpy data. (Mean bond enthalpies/kJmol- $^{-1}:$ C-C $, 347$; $\mathrm{C}=\mathrm{C}, 612 ; \mathrm{C}-\mathrm{H}, 412 .$
(b) The enthalpy change of combustion of liquid benzene at $298 \mathrm{K}$ is $-3267.4 \mathrm{kJmol}^{-1}$. The enthalpy change of vaporization of benzene at $298 \mathrm{K}$ is $+33.9 \mathrm{kJ} \mathrm{mol}^{-1}$
\[
\begin{array}{l}
\left(\mathrm{A}_{1} \mathrm{H}_{298}^{\circ} / \mathrm{kJmol}^{-1}: \mathrm{CO}_{2}(\mathrm{g}),-393.5 ; \mathrm{H}_{2} \mathrm{O}(0,-285.8 ; \mathrm{C}(\mathrm{g})\right. \\
716.7 ; \mathrm{H}(\mathrm{g}), 218 .)
\end{array}
\]

Energy and thermochemistry
Lottie Adams

Enthalpy of reactions

156 Practice Problems
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03:22
Chemistry: Introducing Inorganic, Organic and Physical Chemistry

Use the following bond dissociation enthalpy data to calculate the enthalpy change of formation for HF(g) (Section 25.2)
\[
\begin{array}{l}
D(1-H)=+436 \mathrm{kJmol}^{-1} \\
D_{[F-P]}=+159 \mathrm{kJmol}^{-1} \\
D(1-F)=+570 \mathrm{kJ} \mathrm{mol}^{-1}
\end{array}
\]

Hydrogen
Pronoy Sinha
03:11
Physical Chemistry

The dissociation energies of $\mathrm{HCl}(\mathrm{g}), \mathrm{H}_{2}(\mathrm{g}),$ and $\mathrm{Cl}_{2}(\mathrm{g})$
into normal atoms have been determined spectroscopically and are $4.431,4.476,$ and $2.476 \mathrm{eV},$ respectively. Calculate the enthalpy of formation of $\mathrm{HCl}(\mathrm{g})$ at $0 \mathrm{K}$ in $\mathrm{kJ} \mathrm{mol}^{-1}$ from these data.

Electronic Spectroscopy of Molecules
Lottie Adams
01:59
Atkins' Physical Chemistry

Silylene $\left(\mathrm{SiH}_{2}\right)$ is a key intermediate in the thermal decomposition of silicon hydrides such as silane $\left(\mathrm{SiH}_{4}\right)$ and disilane $\left(\mathrm{Si}_{2} \mathrm{H}_{6}\right) .$ H.K. Moffat et al.
U. Phys. Chem. $95,145(1991)$ ) report $\Delta_{i} H^{\ominus}\left(\mathrm{SiH}_{2}\right)=+274 \mathrm{kJ} \mathrm{mol}^{-1}$. Given that
$\Delta_{1} H^{\ominus}\left(\mathrm{SiH}_{4}\right)=+34.3 \mathrm{kJ} \mathrm{mol}^{-1}$ and $\Delta_{i} H^{\ominus}\left(\mathrm{Si}_{2} \mathrm{H}_{6}\right)=+80.3 \mathrm{kJ} \mathrm{mol}^{-1},$ calculate
the standard enthalpy changes of the following reactions:
(a) $\quad \operatorname{SiH}_{4}(g) \rightarrow \operatorname{SiH}_{2}(g)+H_{2}(g)$
(b) $\quad \operatorname{Si}_{2} \mathrm{H}_{6}(\mathrm{g}) \rightarrow \operatorname{SiH}_{2}(\mathrm{g})+\operatorname{SiH}_{4}(\mathrm{g})$

The First Law
Thermochemistry

Calorimetry

62 Practice Problems
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03:46
Chemistry and Chemical Reactivity

The value of $\Delta U$ for the decomposition of $7.647 \mathrm{g}$ of ammonium nitrate can be measured in a bomb calorimeter. The reaction that occurs is
\[
\mathrm{NH}_{4} \mathrm{NO}_{3}(\mathrm{s}) \rightarrow \mathrm{N}_{2} \mathrm{O}(\mathrm{g})+2 \mathrm{H}_{2} \mathrm{O}(\mathrm{g})
\]
The temperature of the calorimeter, which contains $415 \mathrm{g}$ of water, increases from $18.90^{\circ} \mathrm{C}$ to $20.72^{\circ} \mathrm{C}$
The heat capacity of the bomb is $155 \mathrm{J} / \mathrm{K}$. What is the value of $\Delta U$ for this reaction, in $\mathrm{kJ} / \mathrm{mol}$ ? (IMAGE CANNOT COPY)

Principles of Chemical Reactivity: Energy and Chemical Reactions
Bin Chen
03:48
Introduction to General, Organic and Biochemistry

Heats of reaction are frequently measured by monitoring the change in temperature of a water bath in which the reaction mixture is immersed. A water bath used for this purpose contains 2.000 L of water. In the course of the reaction, the temperature of the water rose $4.85^{\circ} \mathrm{C}$
(a) How many calories were liberated by the reaction?
(b) If $2 \mathrm{kg}$ of a given reactant is consumed in the reaction, how many calories are liberated for each kilogram?

Chemical Reactions and Energy Calculations
Carlene Jimenez
06:44
Chemistry

A hemoglobin molecule (molar mass $=65,000 \mathrm{g}$ ) can bind up to four oxygen molecules. In a certain experiment a $0.085-\mathrm{L}$ solution containing $6.0 \mathrm{g}$ of deoxyhemoglobin (hemoglobin without oxygen molecules bound to it) was reacted with an excess of oxygen in a constant-pressure calorimeter of negligible heat capacity. Calculate the enthalpy of reaction per mole of oxygen bound if the temperature rose by $0.044^{\circ} \mathrm{C}$. Assume the solution is dilute so that the specific heat of the solution is equal to that of water.

Thermochemistry
Rachel Vallejo

Hess’ Law and Enthalpies of formation

53 Practice Problems
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09:25
Chemistry

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 $76 \mathrm{g} / \mathrm{mol},$ calculate its standard enthalpy of formation.

Thermochemistry
Jason Boomer
03:53
Chemistry

From the enthalpy of formation for $\mathrm{CO}_{2}$ and the following information, calculate the standard enthalpy of formation for carbon monoxide (CO).
$$\mathrm{CO}(g)+\frac{1}{2} \mathrm{O}_{2}(g) \longrightarrow \mathrm{CO}_{2}(g) \quad \Delta H^{\circ}=-283.0 \mathrm{kJ} / \mathrm{mol}$$
Why can't we obtain the standard enthalpy of formation directly by measuring the enthalpy of the following reaction?
$$\text { C(graphite) }+\frac{1}{2} \mathrm{O}_{2}(g) \longrightarrow \mathrm{CO}_{2}(g)$$

Thermochemistry
Jason Boomer
02:27
Chemistry

From the standard enthalpies of formation, calculate $\Delta H_{\mathrm{rxn}}^{\circ}$ for the reaction
$$\mathrm{C}_{6} \mathrm{H}_{12}(l)+9 \mathrm{O}_{2}(g) \longrightarrow 6 \mathrm{CO}_{2}(g)+6 \mathrm{H}_{2} \mathrm{O}(l)$$
For $\mathrm{C}_{6} \mathrm{H}_{12}(l), \Delta H_{\mathrm{f}}^{\circ}=-151.9 \mathrm{kJ} / \mathrm{mol}$.

Thermochemistry
Rachel Vallejo

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