“Hess’s law”的概念、定义、翻译、参考文献-科学参考

Hess’s law

Physics

If reactants can be converted into products by a series of reactions, the sum of the heats of these reactions (with due regard to their sign) is equal to the heat of reaction for direct conversion from reactants to products. More generally, the overall energy change in going from reactants to products does not depend on the route taken. The law can be used to obtain thermodynamic data that cannot be measured directly. For example, the heat of formation of ethane can be found by considering the reaction:

$2 C (s) + 3 H_{2} (g) + 3 ½ O_{2} (g) \to 2 {CO}_{2} (g) + 3 H_{2} O (l)$

The heat of this reaction is 2Δ‎H_C+3Δ‎H_H, where Δ‎H_C and Δ‎H_H are the heats of combustion of carbon and hydrogen respectively, which can be measured. By Hess’s law, this is equal to the sum of the energies for two stages:

$2 C (s) + 3 H_{2} (g) \to C_{2} H_{6} (g)$

(the heat of formation of ethane, Δ‎H_f) and

$C_{2} H_{6} (g) + 3 ½ O_{2} \to 2 {CO}_{2} (g) + 3 H_{2} O (l)$

(the heat of combustion of ethane, Δ‎H_E). As Δ‎H_E can be measured and as

$Δ H_{f} + Δ H_{E} = 2 Δ H_{c} + 3 Δ H_{H}$

Δ‎H_f can be found. Another example is the use of the Born–Haber cycle to obtain lattice energies. The law was first put forward in 1840 by the Russian chemist Germain Henri Hess (1802–50). It is sometimes called the law of constant heat summation and is a consequence of the law of conservation of energy.

Chemistry

If reactants can be converted into products by a series of reactions, the sum of the heats of these reactions (with due regard to their sign) is equal to the heat of reaction for direct conversion from reactants to products. More generally, the overall energy change in going from reactants to products does not depend on the route taken. The law can be used to obtain thermodynamic data that cannot be measured directly. For example, the heat of formation of ethane can be found by considering the reactions:
${2 C (s) + 3 H}_{2} (g) + 3 ½ O_{2} (g) \to {2 CO}_{2} (g) + {3 H}_{2} O (l)$
The heat of this reaction is 2Δ‎H_C + 3Δ‎H_H, where Δ‎H_C and Δ‎H_H are the heats of combustion of carbon and hydrogen respectively, which can be measured. By Hess’s law, this is equal to the sum of the energies for two stages:
${2 C (s) + 3 H}_{2} (g) \to C_{2} H_{6} (g)$
(the heat of formation of ethane, Δ‎H_f) and
$C_{2} H_{6} (g) + 3 ½ O_{2} (g) \to {2 CO}_{2} (g) {+ 3 H}_{2} O (l)$
(the heat of combustion of ethane, Δ‎H_E). As Δ‎H_E can be measured and as
$Δ H_{f} + Δ H_{E} = 2 Δ H_{c} + 3 Δ H_{H}$
Δ‎H_f can be found. Another example is the use of the Born-Haber cycle to obtain lattice energies. The law was first put forward in 1840 by the Swiss-born Russian chemist Germain Henri Hess (1802–50). It is sometimes called the law of constant heat summation and is a consequence of the law of conservation of energy.

Chemical Engineering

A law that states that the total heat resulting from a chemical reaction is dependent only on the initial and final states of the reactants and is independent of the reaction route. It is the essential basis of calculations in thermochemistry and has both experimental and theoretical justification. The law is an aspect of the general law of conservation or (p. 182) the first law of thermodynamics. For example, the chemical route of converting calcium oxide (CaO) to calcium chloride (CaCl₂) follows the two routes:
$\begin{array}{l} CaO (s) & \to & + 2 HCl (aq) & \to & {CaCl}_{2} (aq) + H_{2} O (l) \\ {ΔH}_{1} = - 192.5 kJ \\ ↓ & ↑ \\ \begin{array}{l} + H_{2} O (l) \\ {ΔH}_{2} = - 63 kJ \end{array} & \begin{array}{l} + 2 HCl (aq) \\ {ΔH}_{4} = - 117 kJ \end{array} \\ ↓ & ↑ \\ Ca {(OH)}_{2} (s) & \to & + H2O (l) & \to & Ca {(OH)}_{2} (aq) \\ \begin{array}{l} {ΔH}_{3} = - 12.5 kJ \\ {ΔH}_{1} = {ΔH}_{2} + {ΔH}_{3} + {ΔH}_{4} \end{array} \end{array}$

The law is named after Swiss-Russian chemist Germain Henri Hess (1802–50) who pioneered thermochemistry.

单词	Hess’s law
释义	Hess’s law Physics If reactants can be converted into products by a series of reactions, the sum of the heats of these reactions (with due regard to their sign) is equal to the heat of reaction for direct conversion from reactants to products. More generally, the overall energy change in going from reactants to products does not depend on the route taken. The law can be used to obtain thermodynamic data that cannot be measured directly. For example, the heat of formation of ethane can be found by considering the reaction: $2 C (s) + 3 H_{2} (g) + 3 ½ O_{2} (g) \to 2 {CO}_{2} (g) + 3 H_{2} O (l)$ The heat of this reaction is 2Δ‎H_C+3Δ‎H_H, where Δ‎H_C and Δ‎H_H are the heats of combustion of carbon and hydrogen respectively, which can be measured. By Hess’s law, this is equal to the sum of the energies for two stages: $2 C (s) + 3 H_{2} (g) \to C_{2} H_{6} (g)$ (the heat of formation of ethane, Δ‎H_f) and $C_{2} H_{6} (g) + 3 ½ O_{2} \to 2 {CO}_{2} (g) + 3 H_{2} O (l)$ (the heat of combustion of ethane, Δ‎H_E). As Δ‎H_E can be measured and as $Δ H_{f} + Δ H_{E} = 2 Δ H_{c} + 3 Δ H_{H}$ Δ‎H_f can be found. Another example is the use of the Born–Haber cycle to obtain lattice energies. The law was first put forward in 1840 by the Russian chemist Germain Henri Hess (1802–50). It is sometimes called the law of constant heat summation and is a consequence of the law of conservation of energy. Chemistry If reactants can be converted into products by a series of reactions, the sum of the heats of these reactions (with due regard to their sign) is equal to the heat of reaction for direct conversion from reactants to products. More generally, the overall energy change in going from reactants to products does not depend on the route taken. The law can be used to obtain thermodynamic data that cannot be measured directly. For example, the heat of formation of ethane can be found by considering the reactions: ${2 C (s) + 3 H}_{2} (g) + 3 ½ O_{2} (g) \to {2 CO}_{2} (g) + {3 H}_{2} O (l)$ The heat of this reaction is 2Δ‎H_C + 3Δ‎H_H, where Δ‎H_C and Δ‎H_H are the heats of combustion of carbon and hydrogen respectively, which can be measured. By Hess’s law, this is equal to the sum of the energies for two stages: ${2 C (s) + 3 H}_{2} (g) \to C_{2} H_{6} (g)$ (the heat of formation of ethane, Δ‎H_f) and $C_{2} H_{6} (g) + 3 ½ O_{2} (g) \to {2 CO}_{2} (g) {+ 3 H}_{2} O (l)$ (the heat of combustion of ethane, Δ‎H_E). As Δ‎H_E can be measured and as $Δ H_{f} + Δ H_{E} = 2 Δ H_{c} + 3 Δ H_{H}$ Δ‎H_f can be found. Another example is the use of the Born-Haber cycle to obtain lattice energies. The law was first put forward in 1840 by the Swiss-born Russian chemist Germain Henri Hess (1802–50). It is sometimes called the law of constant heat summation and is a consequence of the law of conservation of energy. Chemical Engineering A law that states that the total heat resulting from a chemical reaction is dependent only on the initial and final states of the reactants and is independent of the reaction route. It is the essential basis of calculations in thermochemistry and has both experimental and theoretical justification. The law is an aspect of the general law of conservation or (p. 182) the first law of thermodynamics. For example, the chemical route of converting calcium oxide (CaO) to calcium chloride (CaCl₂) follows the two routes: $\begin{array}{l} CaO (s) & \to & + 2 HCl (aq) & \to & {CaCl}_{2} (aq) + H_{2} O (l) \\ {ΔH}_{1} = - 192.5 kJ \\ ↓ & ↑ \\ \begin{array}{l} + H_{2} O (l) \\ {ΔH}_{2} = - 63 kJ \end{array} & \begin{array}{l} + 2 HCl (aq) \\ {ΔH}_{4} = - 117 kJ \end{array} \\ ↓ & ↑ \\ Ca {(OH)}_{2} (s) & \to & + H2O (l) & \to & Ca {(OH)}_{2} (aq) \\ \begin{array}{l} {ΔH}_{3} = - 12.5 kJ \\ {ΔH}_{1} = {ΔH}_{2} + {ΔH}_{3} + {ΔH}_{4} \end{array} \end{array}$ The law is named after Swiss-Russian chemist Germain Henri Hess (1802–50) who pioneered thermochemistry.
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