HSC Together Year 11 Chemistry: Introduction to Enthalpy and Hess’s Law

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Introduction to Enthalpy and Hess’s Law

Enthalpy and the Law of Conservation of Energy

This post will introduce the first point of the next topic of Module 4 Prelim Chemistry which is enthalpy, Hess’s Law and the law of conservation of energy.

Topic: Enthalpy and Hess’s Law

  • Explain the enthalpy changes in a reaction in terms of breaking and reforming bonds, and relate this to:
    • The law of conservation of energy

 

The Law of Conservation of Energy

The law of conservation of energy states that energy cannot be created nor destroyed only transformed from one form to another (e.g. electricity to mechanical energy). This video will go through the law of conservation of energy in a little more depth.

 

What this tells us is that in a reaction, provided that none is lost to the environment, any heat energy that is put into the reaction will be retained (endothermic) or any heat energy that needs to be released in order for the reaction to proceed (exothermic) will also be conserved as another form. This is also why the magnitude of enthalpy change of the forward and reverse of a reaction is the same except with different signs because one is exothermic (-) and one is endothermic (+).

This short video below gives an example.

 

 

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