(BCR) Demonstration of the Law of Conservation of Matter in Chemical Reactions Lesson

Demonstration of the Law of Conservation of Matter in Chemical Reactions

If you build a campfire like the one above, you start with a big pile of logs. As the fire burns, the pile of logs slowly shrinks. By the end of the evening, all that's left is a small pile of ashes. What happened to the matter that you started with? Was it destroyed by the fire?

It may seem as though burning destroys matter, but the same amount, or mass, of matter still exists after a campfire as before. Look at the picture below. It shows that when wood burns, it combines with oxygen and changes not only to ashes but also to carbon dioxide and water vapor. The gases float off into the air, leaving behind just the ashes. Suppose you had measured the mass of the wood before it burned and the mass of the ashes after it burned. Also, suppose you had been able to measure the oxygen used by the fire and the gases produced by the fire. What would you find? The total mass of matter after the fire would be the same as the total mass of matter before the fire.

This burning campfire example illustrates a very important law in science: law of conservation of matter. This law states that matter cannot be created or destroyed. Even when matter goes through a physical or chemical change, the total mass of matter always remains the same.

How do chemists show the law of conservation of matter? It is demonstrated by all chemical equations being balanced. This means that the same number of each type of atom must appear on both sides of the arrow. In every chemical reaction, the same mass of matter must end up in the products as it started with in the reactants. Balanced chemical equations show that mass is conserved in chemical reactions.

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