However, suppose that you could collect all the oxygen in the air that was combined with the log during the burning and all the smoke and gases that escaped from the burning log and measure their masses, too.In fact, the mass of the ashes is less than that of the log.At first, you might think that matter was lost during this change because the pile of ashes looks much smaller than the log did.Suppose you burn a large log until nothing is left but a small pile of ashes.A similar chemical change produces caves and the icicle shaped rock formations that often are found in them.It changes into a new substance, calcium hydrogen carbonate, which does dissolve in water.However, when the water is even slightly acidic, as it is when it contains some dissolved carbon dioxide, calcium carbonate reacts.Solid calcium carbonate, a compound found in limestone, does not dissolve easily in water.However, the smaller pieces of newly exposed rock still have the same properties as the original sample.Large rocks can split when water seeps into small cracks, freezes, and expands.Do you think these changes, often referred to as weathering, are physical or chemical?.Rocks split, deep canyons are carved out, sand dunes shift, and curious limestone formations decorate caves. The forces of nature continuously shape Earth’s surface.For example, many metals are separated from their ores and then purified using chemical changes. In industry and chemical laboratories, however, this kind of separation is common.You don’t usually separate substances using chemical changes in the home.It can be changed back into silver using a chemical reaction.Tarnish is a chemical reaction between silver metal and sulfur compounds in the air which results in silver sulfide.One case where you might separate substances using a chemical change is in cleaning tarnished silver.The only clue that iron has changed into a new substance is the presence of rust.However, the only sure proof is that a new substance is produced.Clues such as heat, cooling, or the formation of bubbles or solids in a liquid are helpful indicators that a reaction is taking place.The foaming of an antacid tablet in a glass of water and the smell in the air after a thunderstorm are other signs of new substances being produced.A change of one substance to another is a chemical change.EX: reactivity with oxygen, oxygen’s combustibility, a diamond’s resistance to corrosion.
This is an example of how a physical property, such as magnetic attraction, can be used to separate substances in a mixture. The magnet attracts only the iron filings and pulls them from the sand.Every substance has a specific combination of physical properties that make it useful for certain tasks.Attraction to a magnet is a physical property of the substance iron.Some physical properties describe the behavior of a material or a substance.For instance, you could measure the diameter of the ball You can measure some physical properties, too.How would you describe a tennis ball? You could begin by describing its shape, color, and state of matter.
EX: color, shape, size, density, melting point, and boiling point, magnetism.A characteristic of a substance that can be observed without changing its identity.Physical and Chemical Properties and Changes
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