THERMOCHEMISTRY
KEY POINTS:
1. Thermochemistry:
The study of heat change during a chemical reaction is known as thermochemistry.
2. Endothermic reactions:
The chemical reactions, which are accompanied by the absorption of heat, are called endothermic reactions.
3. Enthalpy or heat of solution:
It is defined as the heat change when one mole of a substance is dissolved in a specified number of moles of solvent at a given temperature.
4. Enthalpy:
The total heat content of a system is termed as enthalpy of a system. OR
The enthalpy of a substance is defined as the system's internal enthalpy plus the product of its pressure and volume. (H = E + PV)
5. Endothermic reactions:
The chemical reactions, which are accompanied by the evolution of heat, are called exothermic reactions.
6. State function:
It is a macroscopic property of a system that has some definite value for each state and which is independent of the path or route adopted by the system change rate.
7. Surroundings:
The remaining portions around a system are called surroundings.
8. System:
Anything (materials) under test or under consideration is termed as a system.
9. First law of thermodynamics:
It states that energy can neither be created nor destroyed however it can be changed from one form to another.
10. Irreversible reaction;
An irreversible reaction is that in which products of the reaction do not react to form the original reactants under the same set of conditions.
11. Non-spontaneous process:
It is the reverse of the spontaneous process. It does not take place on its own and does not occur in nature.
12. Reversible reaction:
A reversible reaction is one in which products can react together to form the original reactants.
13. Spontaneous process:
The process which takes place on its own without any outside assistance and moves from a non-equilibrium state towards an equilibrium state is termed a spontaneous process.
14. Heat capacity:
The amount of heat required to raise the temperature of a given amount of a substance by 1 kelvin is called heat capacity.
15. Bond Dissociation energy:
The amount of energy required to break one mole of a particular bond to form neutral atoms is called bond dissociation energy.
16. Standard enthalpy of atomization:
It is the change of enthalpy when one mole of gaseous atoms is formed from the element under standard conditions.
17. Standard enthalpy of formation:
It is the change of enthalpy when one mole of a compound is formed from its elements under standard conditions.
18. Standard enthalpy of neutralization:
It is the amount o heat evolved when one mole of hydrogen ion H+ from an acid reacts with one mole of hydroxide ions OH- form one mole of H2O and alkali under standard conditions.
19. Hess's law of constant heat summation:
If a chemical change takes place by several different routes, the overall energy change is the same, regardless of the route by which the chemical change occurs, provided the initial and final conditions are the same.
20. Calorimeter:
A device that measures heat flow is called a calorimeter.