Key Difference – Law of Conservation of Matter vs Energy
Law of conservation of matter and law of conservation of energy are two laws in chemistry that are used to explain the properties of isolated, closed thermodynamic systems. These laws state that matter or energy cannot be created or destroyed but can be converted to different forms or get rearranged. The key difference between Law of conservation of matter and energy is that the law of conservation of matter states the total mass inside a closed system that does not allow matter or energy to escape should be a constant whereas the law of conservation of energy states energy cannot be created or destroyed, but may be changed from one form to another.
CONTENTS
1. Overview and Key Difference
2. What is Law of Conservation of Matter
3. What is Law of Conservation of Energy
4. Relationship Between Law of Conservation of Matter and Energy
5. Side by Side Comparison – Law of Conservation of Matter vs Energy in Tabular Form
6. Summary
What is Law of Conservation of Matter?
Law of conservation of matter is a principle which describes that the total mass inside a closed system, which does not allow matter or energy to escape, should be a constant. Hence the quantity of mass inside that system is conserved. A system that does not allow energy or matter to pass through its boundary is known as a thermodynamically isolated system.
Figure 1: A comparison Between Isolated, Closed, and Open Thermodynamic Systems
This law also indicates that mass can neither be created nor destroyed, it can only be rearranged or changed from one form to another. These rearrangements or changes occur via chemical reactions. Hence the total mass of reactants is equal to the total mass of products in a chemical reaction that takes place in a closed thermodynamic system. The chemical reactions take place in this closed system can be,
- Nuclear reactions
- Radioactive decay
- Other chemical reactions
What is Law of Conservation of Energy?
The law of conservation of energy is a physical law that states energy cannot be created or destroyed but may be changed from one form to another. In other words, this law indicates that the total energy inside a closed, isolated system remains constant. Hence the energy is conserved within a system.
Figure 2: Sunlight can be Converted into Different Energy Forms, But cannot be Destroyed
For example, the potential energy of the system can be converted to kinetic energy, but cannot be destroyed. This concept can be given in the first law of thermodynamics for a closed thermodynamic system. It can be given as below.
δQ = dU + δW
Where δQ is the amount of energy added to the system, δW is the work lost from the system due thermodynamic work performed by the system and dU is the change in internal energy of the system. This explains that energy is converted into different forms, but not created or destroyed.
What is the Relationship Between Law of Conservation of Matter and Energy?
It is considered that mass can be converted into energy and vice versa. This is the actual way mass-energy conservation occurs. This was first proposed by Henri Poincaré and Albert Einstein, as a concept known as “special relativity”. The relationship between the mass and energy can be given as below:
E = mc2
Where E is the energy, m is the mass and c is the speed of light. However, in classical mechanics, the two laws are considered as separate laws.
What is the Difference Between Law of Conservation of Matter and Energy?
Law of Conservation of Matter vs Energy |
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| Law of conservation of matter is a principle which describes that the total mass should be a constant inside a closed system that does not allow matter or energy to escape. | The law of conservation of energy is a physical law that states energy cannot be created or destroyed but may be changed from one form to another. |
| Conservation | |
| The total mass in an isolated, closed thermodynamic system is conserved. | The total energy in an isolated, closed thermodynamic system is conserved. |
Summary – Law of Conservation of Matter vs Energy
Law of conservation of matter and energy are considered as two separate laws in classical mechanics. But it was later discovered that there is a strong relationship between the two laws. Law of conservation of matter states that the total mass should be a constant inside a closed system that does not allow matter or energy to escape whereas the law of conservation of energy states that energy cannot be created or destroyed, but may be changed from one form to another. This the key difference between law of conservation of matter and energy.
Reference:
1. Helmenstine, Anne Marie. “Law of Conservation of Energy Definition.” ThoughtCo, Nov. 13, 2017, Available here.
2. “Law of Conservation of Matter – Conservation of Mass.” Nuclear Power, Available here.
3. “Conservation of mass.” Wikipedia, Wikimedia Foundation, 19 Feb. 2018, Available here.
Image Courtesy:
1. “Diagram Systems” By Alkh.Alwa – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “Renewable Energy on the Grid” By Kenueone (CC0) via Commons Wikimedia