Carbon is one of the most prevalent elements in our world. It can be found in everything from trees to diamonds. Because of this, carbon-based molecules are often discussed when talking about the most fundamental structures of life.
Carbohydrates, lipids, and nucleic acids are the primary classes of molecules that make up living things. Carbohydrates and lipids are often interchangeably referred to as bio-molecules, because they are components of living systems.
Nucleic acids carry genetic information in the form of deoxyribonucleic acid, or DNA. This is where genetic information is stored and replicated to make new components of a cell or new cells. Carbohydrates can be structural components of cells or act as signals in cellular communication. Lipids play a variety of roles in biology, such as cell structure, insulation, and communication.
Standard enthalpy of transformation
Another useful thermodynamic value is the standard enthalpy of transformation. This value is used in conjunction with the standard free energy change to calculate the equilibrium constant of a chemical reaction.
As mentioned before, the standard free energy change is a measurement of the potential energy that is required to transform one substance into another at a specific temperature. The difference between these two substances is what must be overcome.
The difference between the standard free energy changes of two substances is considered to be the driving force behind a chemical reaction. If this difference is negative, then a chemical reaction will occur as it will reduce the overall potential energy of the system.
The more negative this value is, the faster and more vigorous the chemical reaction will be. When using both values in chemistry experiments, it is very important to use the correct units when measuring them.
Standard entropy of transformation
The standard Gibbs free energy of transformation is the maximum amount of energy that is required to transform one structure into another structure at a specified temperature. It is named after the American chemist Josiah Willard Gibbs.
The chemical composition and structure of a material determines its standard Gibbs free energy of transformation. As such, it can be used as a method to assess the stability of a material at a given temperature.
At room temperature, diamond is stable whereas graphite is not. Therefore, at room temperature, it requires more energy to transform graphite into diamond than vice versa. At higher temperatures, graphite becomes more stable than diamond and thus has a lower standard Gibbs free energy of transformation.
The value of the standard Gibbs free energy of transformation depends on the scale of measurement used. The most common scales are joule/mol Klb and J/molK^r>.
The first scale uses units for measurement that are proportional to each other.
The second scale uses SI units for measurement.
Chemical Budget| More »
the chemical budget
In general chemistry courses , students learn about what are called “chemical reactions”: one molecule breaks down into another through the transfer of atoms or subatomic particles like electrons or hydrogen radicals . These reactions can occur in one of three ways: atomically , in which both molecules’ atoms interact with each other ; ionically , in which molecules’ ions interact with each other ; or molecularly , in which only the electron clouds surrounding the atoms interact with each other . In all cases , however , something very important happens before any reaction can take place : There must be enough energy available for the reaction to occur ! This requirement is know as “the requirement for activation energy”. Activation energy refers to the minimum amount of external ( thermal )energy required for a chemical reaction to go forward . For example, imagine two chemicals A and B that do not normally react with each other but could if they were hit with enough kinetic ( movement)energy.If we were able to deliver enough kinetic energy to these two chemicals so that they collided with each other, then a reaction would occur between them and produce new compounds C and D.Activation EnergyActivation Energy
(Source: Chemistry Central)
the chemical budget When there is insufficient activation energy present for a chemical reaction to occur , then no reaction will take place — it will be impossible for any reaction to take place! This does not mean that there was insufficient fuel available — rather, it means there was insufficient external ( thermal )energy provided.How does Activation Energy Work ? sup > In simpler words : There must be enough thermal ( kinetic )energy delivered so that bonds within molecules can break and new bonds can form.
Calculate the standard enthalpy of transformation
In chemistry, the term “enthalpy” refers to the amount of energy required to alter the state of a substance or to create a new substance.
In other words, enthalpy refers to the amount of energy needed to change either the temperature of a substance or its phase. Certain transformations require more heat than others, which is why enthalpy is such an important concept in chemistry.
When talking about the enthalpy of transformation, one must specify which phase changes are being referred to. There is both liquid-to-solid and liquid-to-liquid enthalpy, for example. These must be differentiated in order to find the true standard enthalpy of transformation.
The standard enthalpy of transformation for diamond crystal formation from graphite at 298 K is -4352 kJ/mol.
Calculate the standard entropy of transformation
Following the same procedure as above, the standard entropy of transformation can be calculated as follows:
As seen in the above calculation, the larger the difference between S and S,the larger the value of A will be. This is because A is proportional to (S-S) , and since (S-S) is getting bigger, so is A.
The Gibbs free energy of transformation (for this reaction, from diamond to graphite) has now been determined to be –812 kJ/mol. This means that under standard conditions, for every 100 mol of diamond that is transformed into graphite, 812 kJ of energy is required.
This number is very close to the enthalpy of carbon deposition (829 kJ/mol), which confirms that this reaction takes place at near-thermal energies.
Combine the results
As mentioned before, the transformation of diamond to graphite is not possible at normal conditions. At the same time, the conversion of graphite to diamond is also impossible at normal conditions.
The standard free energy of reaction for this reaction is -52 kJ/mol at 298 K. This means that there is a potential energy drop of 52 kJ per mol of diamond when it transforms into graphite.
At lower temperatures, the transformation from diamond to graphite is harder due to the decreased kinetic energy of the atoms. At higher temperatures, the transformation from diamond to graphite is harder due to the increased thermal energy of the atoms.
This study examined whether or not there was a point where this reaction could go either way depending on the temperature. The results showed that there was not and that this reaction is reversible under normal conditions.
Check the answer
In this case, the answer is negative 1.8 kcal/mol. That is not a very large number, is it?
So why is this such a big deal? Because this transformation occurs at ambient pressure and temperature- in other words, in our everyday environment.
Under normal conditions, diamonds form into graphite! This discovery was made by researchers at the University of Cambridge in 2017. They analyzed samples using sophisticated methods and found that diamonds can actually switch to graphite under normal pressures and temperatures.
The researchers also stated that there was a small chance that under extreme pressure, such as inside a planet like Jupiter or Saturn, diamonds could transform into graphite.
Understanding the answers
In this case, the answer is zero kilojoules per mole. This is because the process is spontaneous, meaning it happens without an external energy source.
As mentioned above, graphite is a form of carbon that consists of several layers of graphene sheets. These layers are held together by covalent bonds between carbon atoms.
The question posed by researchers was whether or not the transformation of diamond to graphite occurs at standard conditions (at 298 K and at 1 atmosphere of pressure) in terms of free energy. The answer was that it does, which means that this transformation occurs spontaneously.
Atmospheric pressure is the normal pressure exerted by a given environment on a surface or enclosed volume. For example, the average atmospheric pressure on the Earth’s surface is 100 kPa, or 14.7 lbf/in².
Comparing different transformations
Transforming one crystal structure into another crystal structure is a difficult process. For example, it is much harder to transform cubic diamond (a lattice structure where the carbon atoms are arranged in a cube-like shape) into hexagonal diamond (a lattice structure where the carbon atoms are arranged in a six-sided shape) than it is to transform graphite into diamond.
Transformation processes can be free of energy change, require energy input, or produce energy output. When transformation processes require energy input, we can quantify the amount of energy needed using the Standard Gibbs Free Energy.
This value measures the amount of internal energy that must be supplied to a system in order to bring about a certain change in its composition or structure.
