Thermochemical, is one of the branches of chemical science which studies about a change of heat or energy that accompany a chemical reaction, either absorbed or released. The law of conservation of energy states that energy cannot be created or destroyed. Energy can only be transformed from one form to another. Energy can also experience a transfer of the system into the environment or vice versa. The system is all the things that researched the change of energy. Meanwhile, the environment is everything outside the system. An example system and environment can be observed in the water of hot tea in a glass. The tea water is the heat system, while glasses as well as including the environment.
The interaction between the system and the environment can be in the form of exchange of energy or matter. The exchange of this energy can be in the form of heat or other energy forms. The existence of an exchange of energy that cause changes in the amount of energy contained in the system. Based on its interaction with the environment, systems are classified into three types, namely open system, closed system, and isolated system or self.
The System And The Environment Thermochemical
Everything that becomes the center of attention in studying a change in energy and change during that process take place is called with the system. While the things that do not change during the process and which limit the system and can also affect the system is called with the environment
Based on its interaction with the environment, the system is divided into three parts:
A. Open System
Open system i.e. a system that allows to occur a transfer of energy and substance (matter) between the environment with the system. The exchange of the material means that there is a reaction that can leave the reaction vessel, for example a gas
B. closed System
A system where between the system and the environment can occur a transfer of energy, but does not occur exchange of material.
C. isolated System
System teriolasi that is A system that allows the transfer of energy and matter between the system with environment.
The Reaction Of The Thermochemical
The reaction in the thermochemical divided over the reaction is an exothermic reaction and endothermic:
A. The Reaction Of An Exothermic
The reaction that occurs during the heat release or heat. The reaction heat is written with a negative sign.
B. The Reaction Is Endothermic
The reaction that occurs when the ongoing heat absorption or heat, then a change of the enthalpy of reaction is positive.
The Type Of Change Enthalpy
A. The Change Of The Enthalpy Of Formation (ΔHf)
A change enthalpy formation 1 mole compound from its constituent elements at the standard state.
The value of the enthalpy of formation standard specified use the table data the enthalpy of formation standard.
The value of the enthalpy of formation standard:
- Positive, when receiving energy
- Negative value, when the release of energy
- Zero, if the element is already contained in nature naturally
The form of elements in nature is divided into monatomic and poliatomik. Poliatomik means of its constituent elements more than 1 element.
Poliatomiktermasuk halogaen and gas other than noble gas.
All the elements that are already contained in this value the enthalpy of formation of zero.
B. the Change of the enthalpy of decomposition (ΔHd)
Namely ΔH to decompose 1 mole of a compound into its constituent elements at the standard state.
The value of the enthalpy of decomposition of the standard opposite to the value of the enthalpy of formation standard. On the reaction of decomposition of the reactants move to the right and the product is moved to the left.
C. the Change of the enthalpy of combustion (ΔHc)
Namely ΔH in the complete combustion of 1 mole of a compound at the standard state.
The value of the enthalpy of combustion standard determined using table data the enthalpy of combustion standard.
Is the reaction an exothermic
Involving oxygen in the reaction
Carbon terbakan into CO2, burning hydrogen to H2O, and sulfur is burned to SO2.
D. the Change of enthalpy of neutralization (ΔHn)
Including the reaction of an exothermic. that is a the heat is released in the formation of 1 mole of water and acid-base reactions at a temperature of 25 degrees celsius and 1 atmosphere pressure.
- The Change Of Enthalpy Of Neutralization
- Determination Of The Enthalpy Of The Reaction
This determination is performed with:
- Use kalorimetri
- Use Hess's law or the law of summation
- Using the data tables of enthalpy of formation
- Using the data of energy bonding
A. Determination by kalorimetri
Kalorimetri i.e. how the determination of the heat energy of the reaction with the calorimeter. Calorimeter is an isolated system, so that all the energy needed or released to remain in the calorimeter. By measuring the temperature changes.
Description The Formula :
Ql = heat energy in solution (J)
m = mass of substance (kg)
c = heat of substance (J/kg°C)
C = heat capacity (J/°C)
Δt = change in temperature (°C)
Because the calorimeter is an isolated system, then no energy is wasted into the environment, so that the amount of energy the heat of reaction and change in enthalpy of the reaction becomes:
B. the Determination with the data of energy bonding
Bond energy (E) is an energy that is needed to decide on 1 mole of covalent bonds of a compound, each bond requires a different energy that can be interrupted.
The reaction takes place in two stages:
- The severance of the bond of the reactants
- The formation of the bonding product
the formula
Law Related Thermochemical
A. The Law Of Laplace
This law was stated by the Marquis de Laplace (1749-1827), which reads :
“The amount of heat released in the formation of a compound from its elements is equal to the amount of heat required to decompose that compound into its elements”
B. Hess's Law
“If a chemical change can be made some way different, the amount of change of heat energy keselurahannya (total) is fixed, does not depend on the path/way to be taken”.
A reaction can occur via several stages of reaction, and however the stage or the road will not affect the enthalpy of reaction. Change in enthalpy of reaction depends only on the initial state and the end of the system. Not the stage or the road. The change of enthalpy this is the sum of the enthalpy of reaction of each stage.
Thus Hess's law can be used to calculate the ΔH of the reaction based on reaction-another reaction which ΔH is known.
That is review about Thermochemical :
Understanding, System, Reactions, And Formulas Along with Examples For Complete Hopefully what is discussed above is beneficial for the reader. So and thank you.
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