11.5: Enthalpy- Heat of Formation
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- Scott Van Bramer
- Widener University
Learning Objectives
- State the first law of thermodynamics
- Define enthalpy and explain its classification as a state function
- Write and balance thermochemical equations
- Calculate enthalpy changes for various chemical reactions
- Explain Hess’s law and use it to compute reaction enthalpies
Standard Enthalpy of Formation
A standard enthalpy of formation \(ΔH^\circ_\ce{f}\) is an enthalpy change for a reaction in which exactly 1 mole of a pure substance is formed from free elements in their most stable states under standard state conditions. These values are especially useful for computing or predicting enthalpy changes for chemical reactions that are impractical or dangerous to carry out, or for processes for which it is difficult to make measurements. If we have values for the appropriate standard enthalpies of formation, we can determine the enthalpy change for any reaction, which we will practice in the next section on Hess’s law.
The standard enthalpy of formation of CO 2 ( g ) is −393.5 kJ/mol. This is the enthalpy change for the exothermic reaction:
\[\ce{C}(s)+\ce{O2}(g)⟶\ce{CO2}(g)\hspace{20px}ΔH^\circ_\ce{f}=ΔH^\circ_{298}=−393.5\:\ce{kJ} \label{5.4.9}\]
starting with the reactants at a pressure of 1 atm and 25 °C (with the carbon present as graphite, the most stable form of carbon under these conditions) and ending with one mole of CO 2 , also at 1 atm and 25 °C. For nitrogen dioxide, \(\ce{NO}_{2(g)}\), \(ΔH^\circ_\ce{f}\) is 33.2 kJ/mol. This is the enthalpy change for the reaction:
\[\frac{1}{2}\ce{N2}(g)+\ce{O2}(g)⟶\ce{NO2}(g)\hspace{20px}ΔH^\circ_\ce{f}=ΔH^\circ_{298}=+33.2\: \ce{kJ} \label{5.4.10}\]
A reaction equation with \(\frac{1}{2}\) mole of N 2 and 1 mole of O 2 is correct in this case because the standard enthalpy of formation always refers to 1 mole of product, NO 2 ( g ).
You will find a table of standard enthalpies of formation of many common substances in Table \(\PageIndex{1}\) . These values indicate that formation reactions range from highly exothermic (such as −2984 kJ/mol for the formation of P 4 O 10 ) to strongly endothermic (such as +226.7 kJ/mol for the formation of acetylene, C 2 H 2 ). By definition, the standard enthalpy of formation of an element in its most stable form is equal to zero under standard conditions, which is 1 atm for gases and 1 M for solutions.
| Formula | Name | ΔH f (kJ/mol) | Formula | Name | ΔH f (kJ/mol) | |
|---|---|---|---|---|---|---|
| CH 4 (g) | methane | -74.87 | C 5 H 8 (g) | Isoprene | 75.7 | |
| C 2 H 2 (g) | acetylene | 226.73 | C 2 H 5 OH(l) | ethanol | -276. | |
| C 2 H 4 (g) | etylene | 52.47 | CCl 4 (l) | carbon tetrachloride | -128.1 | |
| C 2 H 6 (g) | ethane | -84. | CO(g) | carbon monoxiode | -110.53 | |
| C 3 H 6 (g) | propene | 20.41 | CO 2 (g) | carbon dioxide | -393.51 | |
| C 3 H 8 (g) | propane | -104.7 | H 2 O(g) | water | -241.83 | |
| C 4 H 8 (g) | 1-butene | -0.63 | H 2 O(l) | water | -285.83 | |
| C 4 H 8 (g) | 2-butene | -10.8 | SO 2 (g) | sulfur dioxide | -296.81 | |
| C 4 H 10 (g) | butane | -125.6 | SO 3 (g) | sulfur trioxide | -395.77 | |
| C 4 H 10 (g) | isobutane | -134.2 | H 2 S(g) | dihydrogen sufide | -20.6 | |
| C 8 H 18 (g) | octane | -208.7 | HF(g) | hydrogen fluoride | -273.30 | |
| C 8 H 18 (l) | octane | -250.3 | HCl(g) | hydrogen chloride | -92.31 | |
| C 6 H 6 (l) | benzene | 49. | HBr(g) | hydrogen bromide | -36.29 | |
| C 8 H 12 O 6 (s) | fructose | -1265.6 | HI(g) | hydrogen iodide | 26.5 | |
| C 8 H 12 O 6 ( s) | glucose | -1263.4 | NO(g) | nitrogen monoxide | 90.29 | |
| C 12 H 22 O 11 (s) | Sucrose | -2221.2 | NO 2 (g) | nitrogen dioxide | 33.10 | |
| CH 3 OH(l) | methanol | -238.4 | HNO 3 (aq) | nitric acid | -207.4 |
Example \(\PageIndex{1}\): Evaluating an Enthalpy of Formation
Ozone, O 3 ( g ), forms from oxygen, O 2 ( g ), by an endothermic process. Ultraviolet radiation is the source of the energy that drives this reaction in the upper atmosphere. Assuming that both the reactants and products of the reaction are in their standard states, determine the standard enthalpy of formation, \(ΔH^\circ_\ce{f}\) of ozone from the following information:
S olutio n \(ΔH^\circ_\ce{f}\) is the enthalpy change for the formation of one mole of a substance in its standard state from the elements in their standard states. Thus, \(ΔH^\circ_\ce{f}\) for O 3 ( g ) is the enthalpy change for the reaction:
\[\dfrac{3}{2}\ce{O2}(g)⟶\ce{O3}(g) \nonumber\]
For the formation of 2 mol of O 3 ( g ), \(ΔH^\circ_{298}=+286\: \ce{kJ}\). This ratio, \(\mathrm{\left(\dfrac{286\:kJ}{2\:mol\:O_3}\right)}\), can be used as a conversion factor to find the heat produced when 1 mole of O 3 ( g ) is formed, which is the enthalpy of formation for O 3 ( g ):
Therefore, \(ΔH^\circ_\ce{f}[\ce{O3}(g)]=\ce{+143\: kJ/mol}\).
Exercise \(\PageIndex{1}\)
Hydrogen gas, H 2 , reacts explosively with gaseous chlorine, Cl 2 , to form hydrogen chloride, HCl( g ). What is the enthalpy change for the reaction of 1 mole of H 2 ( g ) with 1 mole of Cl 2 ( g ) if both the reactants and products are at standard state conditions? The standard enthalpy of formation of HCl( g ) is −92.3 kJ/mol.
- Answer
-
For the reaction
\[\ce{H2}(g)+\ce{Cl2}(g)⟶\ce{2HCl}(g)\hspace{20px}ΔH^\circ_{298}=\mathrm{−184.6\:kJ} \nonumber\]
Example \(\PageIndex{2}\): Writing Reaction Equations for \(ΔH^\circ_\ce{f}\)
Write the heat of formation reaction equations for:
- \(\ce{C2H_5OH}_{(l)}\)
- \(\ce{Ca_3(PO_4)}_{2(s)}\)
Solution
Remembering that \(ΔH^\circ_\ce{f}\) reaction equations are for forming 1 mole of the compound from its constituent elements under standard conditions, we have:
- \(\ce{2C}(s,\:\ce{graphite})+\ce{3H2}(g)+\frac{1}{2}\ce{O2}(g)⟶\ce{C2H5OH}(l)\)
- \(\ce{3Ca}(s)+\frac{1}{2}\ce{P4}(s)+\ce{4O2}(g)⟶\ce{Ca3(PO4)2}(s)\)
Note: The standard state of carbon is graphite, and phosphorus exists as \(P_4\).
Exercise \(\PageIndex{2}\)
Write the heat of formation reaction equations for:
- \(\ce{C_2H_5OC_2H}_{5(l)}\)
- \(\ce{Na_2CO}_{3(s)}\)
- Answer a
-
\(\ce{4C}(s,\:\ce{graphite})+\ce{5H2}(g)+\frac{1}{2}\ce{O2}(g)⟶\ce{C2H5OC2H5}(l)\);
- Answer b
-
\(\ce{2Na}(s)+\ce{C}(s,\:\ce{graphite})+\dfrac{3}{2}\ce{O2}(g)⟶\ce{Na2CO3}(s)\)
Hess’s Law
There are two ways to determine the amount of heat involved in a chemical change: measure it experimentally, or calculate it from other experimentally determined enthalpy changes. Some reactions are difficult, if not impossible, to investigate and make accurate measurements for experimentally. And even when a reaction is not hard to perform or measure, it is convenient to be able to determine the heat involved in a reaction without having to perform an experiment.
This type of calculation usually involves the use of Hess’s law, which states: If a process can be written as the sum of several stepwise processes, the enthalpy change of the total process equals the sum of the enthalpy changes of the various steps. Hess’s law is valid because enthalpy is a state function: Enthalpy changes depend only on where a chemical process starts and ends, but not on the path it takes from start to finish. For example, we can think of the reaction of carbon with oxygen to form carbon dioxide as occurring either directly or by a two-step process. The direct process is written:
\[\ce{C}_{(s)}+\ce{O}_{2(g)}⟶\ce{CO}_{2(g)}\;\;\;ΔH^∘_{298}=\mathrm{−394\;kJ} \label{ 5.4.11}\]
In the two-step process, first carbon monoxide is formed:
\[\ce{C}_{(s)}+\dfrac{1}{2}\ce{O}_{2(g)}⟶\ce{CO}_{(g)}\;\;\;ΔH^∘_{298}=\mathrm{−111\;kJ} \label{ 5.4.12}\]
Then, carbon monoxide reacts further to form carbon dioxide:
\[\ce{CO} {(g)}+\dfrac{1}{2}\ce{O2}(g)⟶\ce{CO}_2 {(g)}\;\;\;ΔH^∘_{298}=\mathrm{−283\;kJ} \label{ 5.4.13}\]
The equation describing the overall reaction is the sum of these two chemical changes:
\[\begin {align*} &\textrm{Step 1:} \:\ce{C}(s)+\frac{1}{2}\ce{O2}(g)⟶\ce{CO}(g)\\ &\underline{\textrm{Step 2:} \:\ce{CO}(g)+\frac{1}{2}\ce{O2}(g)⟶\ce{CO2}(g)}\\ &\textrm{Sum:} \:\ce{C}(s)+\frac{1}{2}\ce{O2}(g)+\ce{CO}(g)+\frac{1}{2}\ce{O2}(g)⟶\ce{CO}(g)+\ce{CO2}(g) \end {align*} \label{5.4.14}\]
Because the CO produced in Step 1 is consumed in Step 2, the net change is:
\[\ce{C}_{(s)}+\ce{O}_{2(g)}⟶\ce{CO}_{2(g)} \label{5.4.15}\]
According to Hess’s law, the enthalpy change of the reaction will equal the sum of the enthalpy changes of the steps. We can apply the data from the experimental enthalpies of combustion in Table \(\PageIndex{1}\) to find the enthalpy change of the entire reaction from its two steps:
\[\begin {align*}
&\ce{C}(s)+\frac{1}{2}\ce{O2}(g)⟶\ce{CO}(g)&&ΔH^\circ_{298}=\mathrm{−111\:kJ}\\
&\ce{CO}(g)+\frac{1}{2}\ce{O2}(g)⟶\ce{CO2}(g)&&ΔH^\circ_{298}=\mathrm{−283\:kJ}\\
&\overline{\ce{C}(s)+\ce{O2}(g)⟶\ce{CO2}(g)\hspace{25px}}&&\overline{ΔH^\circ_{298}=\mathrm{−394\:kJ}}
\end {align*} \label{5.4.16}\]
The result is shown in Figure \(\PageIndex{6}\). We see that ΔH of the overall reaction is the same whether it occurs in one step or two. This finding (overall ΔH for the reaction = sum of Δ H values for reaction “steps” in the overall reaction) is true in general for chemical and physical processes.
Before we further practice using Hess’s law, let us recall two important features of Δ H .
-
Δ
H
is directly proportional to the quantities of reactants or products. For example, the enthalpy change for the reaction forming 1 mole of NO
2
(
g
) is +33.2 kJ: \[\frac{1}{2}\ce{N2}(g)+\ce{O2}(g)⟶\ce{NO2}(g)\hspace{20px}ΔH=\mathrm{+33.2\: kJ} \label{5.4.17}\]
When 2 moles of NO 2 (twice as much) are formed, the Δ H will be twice as large: \[\ce{N2}(g)+\ce{2O2}(g)⟶\ce{2NO2}(g)\hspace{20px}ΔH=\mathrm{+66.4\: kJ} \label{5.4.18}\]
In general, if we multiply or divide an equation by a number, then the enthalpy change should also be multiplied or divided by the same number.
-
Δ
H
for a reaction in one direction is equal in magnitude and opposite in sign to Δ
H
for the reaction in the reverse direction. For example, given that: \[\ce{H2}(g)+\ce{Cl2}(g)⟶\ce{2HCl}(g)\hspace{20px}ΔH=\mathrm{−184.6\:kJ} \label{5.4.19}\]
Then, for the “reverse” reaction, the enthalpy change is also “reversed”: \[\ce{2HCl}(g)⟶\ce{H2}(g)+\ce{Cl2}(g)\hspace{20px}ΔH=\mathrm{+184.6\: kJ} \label{5.4.20}\]
Here is a less straightforward example that illustrates the thought process involved in solving many Hess’s law problems. It shows how we can find many standard enthalpies of formation (and other values of Δ H ) if they are difficult to determine experimentally.
Example \(\PageIndex{3}\): S t epwise Calculation of \(ΔH^\circ_\ce{f}\)
Using Hess’s Law Determine the enthalpy of formation, \(ΔH^\circ_\ce{f}\), of FeCl 3 (s) from the enthalpy changes of the following two-step process that occurs under standard state conditions:
\[\ce{Fe}(s)+\ce{Cl2}(g)⟶\ce{FeCl2}(s)\hspace{20px}ΔH°=\mathrm{−341.8\:kJ} \nonumber\]
\[\ce{FeCl2}(s)+\frac{1}{2}\ce{Cl2}(g)⟶\ce{FeCl3}(s)\hspace{20px}ΔH°=\mathrm \nonumber{−57.7\:kJ} \]
Solution
We are trying to find the standard enthalpy of formation of FeCl3(s), which is equal to ΔH° for the reaction:
\[\ce{Fe}(s)+\frac{3}{2}\ce{Cl2}(g)⟶\ce{FeCl3}(s)\hspace{20px}ΔH^\circ_\ce{f}=\:? \nonumber\]
Looking at the reactions, we see that the reaction for which we want to find Δ H ° is the sum of the two reactions with known Δ H values, so we must sum their Δ H s:
\[\ce{Fe}(s)+\ce{Cl2}(g)⟶\ce{FeCl2}(s)\hspace{59px}ΔH°=\mathrm{−341.8\:kJ}\\ \underline{\ce{FeCl2}(s)+\frac{1}{2}\ce{Cl2}(g)⟶\ce{FeCl3}(s)\hspace{20px}ΔH°=\mathrm{−57.7\:kJ}}\\ \ce{Fe}(s)+\frac{1}{2}\ce{Cl2}(g)⟶\ce{FeCl3}(s)\hspace{43px}ΔH°=\mathrm{−399.5\:kJ} \nonumber\]
The enthalpy of formation, \(ΔH^\circ_\ce{f}\), of FeCl 3 (s) is −399.5 kJ/mol.
Exercise \(\PageIndex{3}\)
Calculate ΔH for the process:
\[\ce{N2}(g)+\ce{2O2}(g)⟶\ce{2NO2}(g) \nonumber\]
from the following information:
\[\ce{N2}(g)+\ce{O2}(g)⟶\ce{2NO}(g)\hspace{20px}ΔH=\mathrm{180.5\:kJ} \nonumber\]
\[\ce{NO}(g)+\frac{1}{2}\ce{O2}(g)⟶\ce{NO2}(g)\hspace{20px}ΔH=\mathrm{−57.06\:kJ} \nonumber\]
- Answer
-
66.4 kJ
Hess's Law and Heat of Formation
We also can use Hess’s law to determine the enthalpy change of any reaction if the corresponding enthalpies of formation of the reactants and products are available. The stepwise reactions we consider are: (i) decompositions of the reactants into their component elements (for which the enthalpy changes are proportional to the negative of the enthalpies of formation of the reactants), followed by (ii) re-combinations of the elements to give the products (with the enthalpy changes proportional to the enthalpies of formation of the products).
Example \(\PageIndex{4}\): Using Hess’s Law
What is the standard enthalpy change for the reaction:
\[\ce{3NO2}(g)+\ce{H2O}(l)⟶\ce{2HNO3}(aq)+\ce{NO}(g)\hspace{20px}ΔH°=\:? \nonumber\]
Solving with Hess's Law and Heat of Formation
We can write this reaction as the sum of the decompositions of 3NO 2 ( g ) and 1H 2 O( l ) into their constituent elements, and the formation of 2 HNO 3 ( aq ) and 1 NO( g ) from their constituent elements. Writing out these reactions, and noting their relationships to the \(ΔH^\circ_\ce{f}\) values for these compounds (from Tables T1 and T2 ), we have:
\[\ce{3NO2}(g)⟶ \dfrac{3}{2} \ce{N2}(g)+ 3 \ce{O2}(g)\hspace{20px}ΔH^\circ_{1}=\mathrm{−99.6\:kJ} \nonumber\]
\[\ce{H2O}(l)⟶\ce{H2}(g)+\frac{1}{2}\ce{O2}(g)\hspace{20px}ΔH^\circ_{2}=+285.8\: \ce{kJ}\:[−1×ΔH^\circ_\ce{f}(\ce{H2O})] \nonumber\]
\[\ce{H2}(g)+\ce{N2}(g)+ 3 \ce{O2}(g)⟶\ce{2HNO3}(aq)\hspace{20px}ΔH^\circ_{3}=−414.8\:kJ\:[2×ΔH^\circ_\ce{f}(\ce{HNO3 \nonumber})]\]
\[\frac{1}{2}\ce{N2}(g)+\frac{1}{2}\ce{O2}(g)⟶\ce{NO}(g)\hspace{20px}ΔH^\circ \nonumber_{4}=+90.2\: \ce{kJ}\:[1×(\ce{NO})]\]
Summing these reaction equations gives the reaction we are interested in:
\[\ce{3NO2}(g)+\ce{H2O}(l)⟶\ce{2HNO3}(aq)+\ce{NO}(g) \nonumber\]
Summing their enthalpy changes gives the value we want to determine:
\[\begin {align*} ΔH^\circ_\ce{rxn}&=ΔH^\circ_1+ΔH^\circ_2+ΔH^\circ_3+ΔH^\circ_4=\mathrm{(−99.6\:kJ)+(+285.8\: kJ)+(−414.8\:kJ)+(+90.2\: kJ)}\\ &=\mathrm{−138.4\:kJ} \end {align*}\]
So the standard enthalpy change for this reaction is Δ H ° = −138.4 kJ.
Note that this result was obtained by:
- multiplying the \(ΔH^\circ_\ce{f}\) of each product by its stoichiometric coefficient and summing those values,
- multiplying the \(ΔH^\circ_\ce{f}\) of each reactant by its stoichiometric coefficient and summing those values, and then
- subtracting the result found in step 2 from the result found in step 1.
Setting up Hess's Law Problems using a Reaction Table.
An easy way to set up these problems is with a reaction table. Below each reactant and product write the ΔH^\circ_\ce{f} value from the table above. In the next row change the sign of ΔH^\circ_\ce{f} value each reactant, since you are decomposing the reactants NOT forming them. And multiply the ΔH^\circ_\ce{f} value by the stoichiometric coefficent to account for the number of moles for each reactant and product.
| \(\ce{3NO2}(g) \) | \(\ce{H2O}(l) \) | ⟶ | \(\ce{2HNO3}(aq) \) | \(\ce{NO}(g) \) | |
| \( ΔH^\circ_\ce{f} (kJ) \) | 33.2 | -285.83 | -207.4 | 90.2 | |
| \( ΔH^\circ_\ce{rxn} (kJ) \) | -99.6 | +285.83 | -414.8 | 90.2 |
After the table is set up, just combine the values in the last row to find \( ΔH^\circ_\ce{rxn} = -138.4 kJ \)
Setting up Hess's Law Problems using the sums equation.
The standard enthalpy change of the overall reaction is therefore equal to: (ii) the sum of the standard enthalpies of formation of all the products plus (i) the sum of the negatives of the standard enthalpies of formation of the reactants. This is usually rearranged slightly to be written as follows, with \(\sum\) representing “the sum of” and n standing for the stoichiometric coefficients:
\[ΔH^\circ_\ce{reaction}=\sum n×ΔH^\circ_\ce{f}\ce{(products)}−\sum n×ΔH^\circ_\ce{f}\ce{(reactants)} \label{5.4.20B}\]
The following example shows in detail why this equation is valid, and how to use it to calculate the enthalpy change for a reaction of interest.
The solution to this is as follows:
\[ΔH^\circ_\ce{reaction}=∑n×ΔH^\circ_\ce{f}\ce{(products)}−∑n×ΔH^\circ_\ce{f}\ce{(reactants)} \nonumber\]
\[\begin {align*} &=\mathrm{\left[2\:\cancel{mol\:HNO_3}×\dfrac{−207.4\:kJ}{\cancel{mol\:HNO_3\:(\mathit{aq})}}+1\:\cancel{mol\: NO\:(\mathit{g})}×\dfrac{+90.2\: kJ}{\cancel{mol\: NO\:(\mathit{g})}}\right]}\\ &\mathrm{\:−\,\left[3\:\cancel{mol\:NO_2(\mathit{g})}×\dfrac{+33.2\: kJ}{\cancel{mol\:NO_2\:(\mathit{g})}}+1\:\cancel{mol\:H_2O\:(\mathit{l})}×\dfrac{−285.8\:kJ}{\cancel{mol\:H_2O\:(\mathit{l})}}\right]}\\ &=\mathrm{2(−207.4\:kJ)+1(+90.2\: kJ)−3(+33.2\: kJ)−1(−285.8\:kJ)}\\ &=\mathrm{−138.4\:kJ}\end {align*}\]
Exercise \(\PageIndex{4}\)
Calculate the heat of combustion of 1 mole of ethanol, C 2 H 5 OH( l ), when H 2 O( l ) and CO 2 ( g ) are formed. Use the following enthalpies of formation: C 2 H 5 OH( l ), −278 kJ/mol; H 2 O( l ), −286 kJ/mol; and CO 2 ( g ), −394 kJ/mol.
- Answer
-
−1368 kJ/mol
This project was preformed to supply Libretext Authors with videos on General Chemistry topics which can be used to enhance their projects. Also, these videos are meant to act as a learning resource for all General Chemistry students .
Video Topics
The enthalpy of an unknown reaction can be found using the equation: ΔH° = Sum of VΔHf°(product) - Sum of VΔHf°(reactants). ΔHf is the enthalpy of formation for a given species. V is the stoichiometric coefficient of the species from the balanced reaction. Remember that ΔHf° = 0 for elements in their reference states. This video contains a sample problem, which involves these concepts.
Link to Video
Calculating H° using Hf°: https://youtu.be/Y3aJJno9W2c
Summary
If a chemical change is carried out at constant pressure and the only work done is caused by expansion or contraction, q for the change is called the enthalpy change with the symbol Δ H , or \(ΔH^\circ_{298}\) for reactions occurring under standard state conditions. The value of Δ H for a reaction in one direction is equal in magnitude, but opposite in sign, to Δ H for the reaction in the opposite direction, and Δ H is directly proportional to the quantity of reactants and products. Examples of enthalpy changes include enthalpy of combustion, enthalpy of fusion, enthalpy of vaporization, and standard enthalpy of formation. The standard enthalpy of formation, \(ΔH^\circ_\ce{f}\), is the enthalpy change accompanying the formation of 1 mole of a substance from the elements in their most stable states at 1 bar (standard state). Many of the processes are carried out at 298.15 K. If the enthalpies of formation are available for the reactants and products of a reaction, the enthalpy change can be calculated using Hess’s law: If a process can be written as the sum of several stepwise processes, the enthalpy change of the total process equals the sum of the enthalpy changes of the various steps.
Glossary
- enthalpy ( H )
- sum of a system’s internal energy and the mathematical product of its pressure and volume
- enthalpy change (Δ H )
- heat released or absorbed by a system under constant pressure during a chemical or physical process
- first law of thermodynamics
- internal energy of a system changes due to heat flow in or out of the system or work done on or by the system
- Hess’s law
- if a process can be represented as the sum of several steps, the enthalpy change of the process equals the sum of the enthalpy changes of the steps
- hydrocarbon
- compound composed only of hydrogen and carbon; the major component of fossil fuels
- internal energy ( U )
- total of all possible kinds of energy present in a substance or substances
- standard enthalpy of formation (\(ΔH^\circ_\ce{f}\))
- enthalpy change of a chemical reaction in which 1 mole of a pure substance is formed from its elements in their most stable states under standard state conditions
- standard state
- set of physical conditions as accepted as common reference conditions for reporting thermodynamic properties; 1 bar of pressure, and solutions at 1 molar concentrations, usually at a temperature of 298.15 K
- state function
- property depending only on the state of a system, and not the path taken to reach that state
Contributors and Attributions
-
Paul Flowers (University of North Carolina - Pembroke), Klaus Theopold (University of Delaware) and Richard Langley (Stephen F. Austin State University) with contributing authors. Textbook content produced by OpenStax College is licensed under a Creative Commons Attribution License 4.0 license. Download for free at http://cnx.org/contents/85abf193-2bd...a7ac8df6@9.110 ).