1st Year Chemistry Chapter 7 Notes
Important Complete Computerized 1st Year Chemistry Chapter 7 Notes written by Honorable Professor Mr. Faraz Qadir Suib. These notes are very helpful in the preparation of Thermochemistry of 1st Year Chemistry Chapter 7 Notes for the students of the intermediate and these are according to the paper patterns of all Punjab boards.
Summary and Contents:
Topics which are discussed in the notes are given below:
- Internal Energy and First Law of Thermodynamics
- Measurement of Internal energy
- Ways to transfer energy
- There are two fundamental ways of transferring energy to or from a system.
- Type of work in thermochemistry
- State with experimental of First Law of Thermodynamics
- Glass Calorimeter and Enthalpy of Neutralization: It is used to determine the enthalpy of neutralization. It determines the value of ∆H.
Enthalpy of Neutralization
The standard enthalpy of neutralization is the amount of heat evolved when one mole of hydrogen ions [H+
]
from an acid, react with one mole of hydroxide ions from a base to form one mole of water. For example, the
enthalpy of neutralization of sodium hydroxide by hydrochloric (OH-
) acid is -57.4 kJ mol-1
.
Assembly
Following are the key features of the assembly of glass calorimeter:
1. This usual type of calorimeter is basically an insulated container. To serve the purpose of insulation broken
pieces of glass or cotton wool is used.
2. It has a thermometer.
3. It has a stirrer.
- state and explain hess's law of constant heat summation
- Purpose of Bomb Calorimeter: A bomb calorimeter is usually used for the accurate determination of the enthalpy of combustion for food, fuel
and other compounds.
Enthalpy of combustion
The standard enthalpy of combustion of the substance is the amount of heat evolved when one mole of the
substance is completely burnt in excess of oxygen under standard conditions. It is denoted by ∆H oC.
Example
Standard enthalpy of combustion of ethanol ∆H ⁰C is -1368 kJ mol-1
.
Assembly
Following are the key features of assembly of bomb calorimeter:
1. It consists of a strong cylindrical steel vessel
2. It is lined with enamel to prevent corrosion.
3. It is provided with a thermometer and a stirrer.
4. Platinum crucible is inside the steel bomb to hold the sample.
5. Ignition coil is also provided.
- Enthalpy of combustion with example
- State and explain of hess 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.
Explanation
For many reactions, ΔH cannot be measured directly by calorimetric method.
Examples
1. Preparation of tetrachloromethane (CCl4) from carbon and chlorine.
2. Decomposition of tetrachloromethane into its constituent elements.
3. Boron oxide (B2O3) and aluminium oxide (Al2O3) provide problems for the measurement of standard
enthalpies of their formation as it is difficult to burn these elements completely in oxygen because a protective
layer of oxides covers the surface of the unreacted element.
4. Heat of formation of CO cannot be measured directly due to the formation of CO2 with it.
- State and explain of The Born-Haber Cycle
- Define Enthalpy and prove that ∆H= qp
- State and explain Hess’s law of constant heat summation.
- State 1st law of thermodynamics. Prove that ∆E=qv
- Define Enthalpy of reaction. How is it measured by Glass Calorimeter?
- What is molar heat of combustion? How is it measured by bomb calorimeter?