Matter and Energy

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  1. Describe the conservation of mass
  2. Briefly discuss the basic biochemical reactions
  3. Discuss the first and second laws of thermodynamics, especially as they related to the environment


Everything in the world can be divided into two things:

  • Matter
  • Energy
anything that has mass and takes up space

Conservation of Mass

Conservation of Mass

All mass is conserved - it is neither created nor destroyed.
It may however, change forms

Chemical Reactions

Chemical reaction 
chemicals recombining to form other chemicals is called a chemical reaction

Reactions which release heat are called exothermic.

Reactions which absorb heat are called endothermic.

All of life processes are actually chemical reactions. The two most important of these are photosynthesis and respiration


The process which plants use to create glucose from carbon dioxide and water

Glucose is the simplest sugar and the building block for all higher carbohydrates.

This reaction requires light. Such a reaction is called a photochemical reaction.


Use of oxygen to break down complex chemicals and release energy

Respiration is what provides energy for other process to occur.


force acting through a distance
the capacity to do work
energy transferred due to a temperature difference

All of nature is driven by energy. How this energy flows through the environment is important. The ultimate source of this energy is the SUN.

The flow of energy is governed by the two laws of thermodynamics.

First law of thermodynamics

Energy is never destroyed or created
There is no free lunch


you need fuel to keep your car running
you need food to keep yourself running

Second Law


  • How do we uncook rice?
  • How do we unpeel an orange?

First law says cooking and uncooking are exactly the same.

These questions lead to the second law of thermodynamics.

Second law of thermodynamics

No system can completely convert heat to work
All systems tend toward disorder
You cannot break even

The measure of disorder is called the Entropy

The second law therefore says that the total entropy will always increase.

Since heat cannot be entirely converted to work, we say heat is lower quality than work. Whenever energy is converted from one form to another, some is lost as heat.

As we said before energy flows through the environment starting with energy from the sun. However, by the second law this energy gradually loses its quality.

Whenever energy is transformed some energy is lost as heat (waste heat)

The percentage of energy transferred as useful work is called the efficiency.


  • Electrical Power Plant 30%
  • Fuel Cell 60%
  • Human Body 25%
  • Fluorescent Light 15%
  • Car Engine 10%
  • Incandescent Light 5%

In food chains the efficiency of each level is about 5 - 20%. Carnivores have about 1% of the energy that plants capture.

Energy flow through a food chain

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Thermodynamics - A wikieducator project on this topic