physical and chemical changes third year level preciosa v. cabrera ismael mathay sr. high school

PHYSICAL AND CHEMICAL CHANGES

Third Year Level

Preciosa V. CabreraIsmael Mathay Sr. High School

Objectives:

Preciosa V. Cabrera Ismael Mathay Sr. High School 10/16/09

At the end of the lesson, the students should be able to:

1. Differentiate physical change from chemical change.

2. Describe what happens to a substance that undergoes chemical change.

3. Identify the signs of chemical change in a reaction.

Properties of Matter

Physical properties: • do not change the chemical nature of matter.• examples: color, smell, freezing point, boiling

point, temperature, density, viscosity Chemical properties: • change the chemical nature of matter.• examples: heat of combustion, reactivity with

another substance, toxicity, flammability


•anything that has mass and volume

To understand changes in matter, you need to be able to describe and classify the sample• before the change and• after the change

Matter


• Physical change

• Chemical change

There are two changes in matter


• occur when a substance changes its appearance without changing its composition.

• phase change.

Physical Changes


Phase changes in matter

http://www.clickandlearn.org/images/water_cycle.gif


Chemical Changes

http://www.ric.edu/faculty/ptiskus/chemical/

Chemical changes are changes substances undergo when they become new or different substances. Preciosa V. Cabrera Ismael Mathay Sr. High School 10/16/09

The fireworks we see during New Year’s Eve are actually metals such as magnesium and copper that change chemically as they light up the night skies with their fantastic colors.

Fireworks


Evidences of Chemical Change

• Change in intensive

properties such as

odor, color and taste


Change in temperature


Formation of a solid substance or precipitate



Production of heat or light



Production of mechanical energy


paper

Evolution of gas or formation of bubbles


Production of electrical energy


Activity

Materials: pieces of paper test tubes styrofoam watch glass acetone pair of scissors vinegar dropper NaHCO3 match milk modeling clay


Procedure


2. Mold the modeling clay into different shapes. Observe.

3. Cut the styrofoam into pieces. Place the cut styrofoam in the watch glass and add a few drops of acetone. Observe what happens.


4. Put about 10 mL of vinegar in two test tubes. Add a pinch of sodium bicarbonate in one test tube and 5 mL of milk in another. Observe what happens in both test tubes.

5. Enter your observations in the table below.


Data and Observation

System Observation Physical or Chemical change

Signs of Chemical change

1. Cutting paper

2. Burning paper

3. Molding clay

4. Cutting Styrofoam

5. Styrofoam and acetone

6. Vinegar and NaHCO3

7. Vinegar and milk


1. Can physical and chemical changes occur in a system at the same time?

2. What is the difference between a physical change chemical change?

3. What patterns of evidence do you note in your observations of physical change? of chemical change?

A. Guide questions


1. formation of clouds2. burning of plastic3. corrosion of iron 4. sublimation of iodine crystals5. decaying of food

B. Identify the type of change. Justify your answer.


Summary of the lesson

Physical Change

There is only a change in phase

Change in the appearance of the substance

Chemical Change

Change in the

properties of the

substance. The substances

formed are different from the original substance.


Original substance can be recovered

The substances are the same before and after the change

Original substance can not be recovered

The substances are not the same before and after the change

physical and chemical changes third year level preciosa v. cabrera ismael mathay sr. high school

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