conservation of mass

law of conservation of mass

This burning campfire example illustrates a very important law in science: the law of conservation of mass. 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. Q: How could you show that the mass of matter remains the same when matter changes state? A: You could find the mass of a quantity of liquid water. Then you could freeze the water and find the mass of the ice. The mass before and after freezing would be the same, showing that mass is conserved when matter changes state.

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wheres the matter

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 sketch in Figure 1.1. 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. Q: What can you infer from this example? A: You can infer that burning does not destroy matter. It just changes matter into different substances.

instructional diagrams

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questions

mass is conserved in physical but not chemical changes in matter.

a. true

-->  b. false

when you burn a candle, all that remains is a small puddle of wax. the puddle of wax has less mass than the original candle. the rest of the original candles mass was

a) destroyed.

-->  b) changed to gases.

c) measured incorrectly.

d) none of the above

an astronaut weighs much less on the moon than on earth because he has much less mass on the moon.

a. true

-->  b. false

fire destroys the mass of the fuel that it burns.

a. true

-->  b. false

the products of a chemical reaction can never have greater mass than the reactants.

-->  a. true

b. false

diagram questions

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