Physical and Chemical Changes

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Physical and Chemical Changes

Change… change is good! Some of the most important uses for substances are those that result from change. E.g. applying heat to cook an egg, freezing water to make an ice rink

Physical Changes

• The substance involved in the physical change remains the same

• It may change state or form, all changes of state are physical changes

• Most physical changes can be reversed

How many changes of state can you observe in the candle wax when it is burning?

Chemical Changes

• The original substance is changed into one or more different substances

• The new substances have different properties from the original substance

• Most chemical changes are difficult to reverse

• Often you can not “see” the chemical change, but you can observe the results of the change

Chemical Change CluesA new colour appears

Heat or light is given off

Bubbles of gas are formed

A solid material (called a precipitate) forms in a liquid

Everyday Chemical Change

Think about your environment, do you see chemical changes occurring around you?

What sort of chemical changes occur at McDonalds when they cook you a hamburger?

1. The hamburger turns brown from pink when cooked, does that mean chemical or physical change?

2. The bun gets toasted and turns brown from white. (chemical or physical)

3. Tomato's are chopped for the burger. (chemical/physical)

4. The burger is wrapped in paper. (chemical/physical)

Everyday Chemical ChangesAre there chemical changes that occur that aren’t good?In the auto industry, car’s are made out of metal. What happens when a car gets older and the paint chips?This is called corrosion (or rusting). Corrosion is the slow chemical reaction of a metal with oxygen. Rusting: involves the corrosion of iron. When iron reacts with oxygen in the air or water, iron oxide is produced. This chemical change costs the auto industry millions of dollars a year in damage to vehicles.

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How can we stop metal from rusting?

Rust is damaging because it is porous and absorbs water. This causes the rust to flake off, exposing fresh metal to oxygen and this process continues until rust has eaten its way through the metal.

Preventing Corrosion: • Exposed metal can be painted• Spray underneath cars with oil• Use materials that do not react chemically with

oxygen in the air (e.g. car bumpers)

Lab Activity

• Open up the word document“3b – Observing Changes in Kitchen Chemistry”

• Print out the document double sided and ask your teacher for materials to do the experiment.

• Be sure to read the experiment completely before asking your teacher for the materials.