Enthalpy Change ∆H Of A Reaction - Reaction Enthalpy
Chapter Name : Thermodynamics |
Sub Topic Code : 102_11_06_04_06 |
Topic Name : Enthalpy Change ∆H Of A Reaction - Reaction Enthalpy |
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Sub Topic Name : Hess's Law Of Constant Heat Summation |
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Introduction
·
Hess’s law states that enthalpy change does not depend
on the path taken by the reaction, only the enthalpy of the initial and final
state.
?H = ?H1 +
?H2
·
Enthalpy is thus considered to be
a state function.
·
Hess’s law helps
determine the heat of formation or transformation of a chemical reaction.
Pre-Requisites:
·
Thermodynamic
terms
·
The state of a
system
·
Enthalpy
Activity:
when you add salt or sugar to water or add water
to sugar and salt: the end result is the same: therefore the process is path
independent.
Real Life Question:
How to calculate
enthalpy of formation or transformation of a chemical reaction?
Key Words / FlashCards
| Key Words | Definitions (pref. in our own words) |
|---|---|
| Enthalpy | It is same as energy at low and moderate pressure |
| Hess’s law | It states that the enthalpy change does not depend on the path taken by the reaction, only the enthalpy of the initial and final state. |
Learning aids / Gadgets
| Gadgets | How it can be used |
|---|---|
| Salt water | Adding salt to water or adding water to salt gives the same result: salty water: therefore it is path independent. |
Real life uses :
Hess’s law helps calculate :
-
The enthalpy of formation of chemical reactions
The
enthalpy of transformation of allotrope of elements.
Places to visit :
kitchen
Practical examples around us
| Examples | Explainations |
|---|---|
| Salt or sugar water | when you add salt or sugar to water or add water to sugar and salt: the end result is the same: therefore the process is path independent. |
What you learn in Theory:
Calculation of
formation or transformation enthalpy of chemical reactions.
What you learn in Practice:
Enthalpy change is
path independent.