Also suppose we had been able to measure the oxygen used by the fire and the gases produced by the fire. Suppose we had measured the mass of the wood before it burned and the mass of the ashes after it burned. The gases float off into the air, leaving behind just the ashes. Figure 5.1.1 shows that when wood burns, it combines with oxygen and changes not only to ashes, but also to carbon dioxide and water vapor. It may seem as though burning destroys matter, but the same amount, or mass, of matter still exists after a campfire as before. According to the law of conservation of matter, matter is neither created nor destroyed, so we must have the same number and kind of atoms after the chemical change as were present before the chemical change. Both the initial and final substances are composed of atoms because all matter is composed of atoms. What does this mean for chemistry? In any chemical change, one or more initial substances change into a different substance or substances. \): \(4.4 \,g+ 5.6\, g = 10\, g\).īecause the mass of the reactants = the mass of the products, the observations are in agreement with the law of conservation of mass.
