Science Module8th Grade

TAKS Objective 3 – The student will demonstrate an understanding of the structures and properties of matter.

• Complex interactions occur between matter and energy.

TEKS 8.10 (C)

The student knows that complex interactions occur between matter and energy. The student is expected to:

identify and demonstrate that loss or gain of heat energy occurs during exothermic and endothermic chemical reactions.

Learning Objectives

1. identify endothermic and exothermic reactions associated with chemical changes

2. Explain the loss or gain of heat during chemical reactions

3. Identify chemical and physical changes associated with endothermic and exothermic reactions

Background

Heat- transfer of energy

Exothermic- heat energy EXITS the system- ex. Combustion, evaporation of water- surroundings usually feel warmer

Salt

An example of an exothermic reaction is the mixture of sodium metal and chlorine gas which yields table salt.

2Na(s) + Cl2(g) 2NaCl(s) + energy

Endothermic- heat energy ENTERS the system- ex. Cold packs, melting ice- surroundings usually feel cooler

How do cold packs work?

The outer pouch contains water. The inner pouch contains ammonium-nitrate.

When you “pop” the inner pouch, the chemical reaction absorbs heat energy from the surroundings. This is an endothermic reaction.

The temperature of the solution falls to about 35 F for 10 to 15 minutes.

Photosynthesis

During photosynthesis, plants absorb the energy from the sun to convert carbon dioxide and water into glucose and oxygen.

sunlight + 6CO2(g) + 6H2O(l) C6H12O6(aq) + 6O2(g)

Physical change- change in size, shape or state of matter

Chemical Reaction - process in which one or more substances are changed into others. Chemical reactions are accompanied by a loss or gain of energy.

True or False

Chemical reactions always produce heat

Chemical reactions can release orabsorb heat, but can also create

light, sound or electricity!

True or False

Heat can be lost, destroyedor just disappear

Heat energy is transferred from one object to another, or is transferred to another form of energy, but never disappears.

Law of Conservation of Energy

True or False

Color change is always a physical property

Color is a physical property.

Color change can be the resultof a chemical change.

ENGAGE• Cold Packs• Rubber Bands• Glo-sticks

EXPLORE• Hot or Not

– students explore endothermic and exothermic chemical reactions using baking soda and calcium chloride

EXPLAIN

1. List 3 physical properties of matter.

2. List 3 physical properties for:• Calcium chloride• Baking soda• Phenol red solution

3. Describe what happens with baking soda and calcium chloride are mixed.

4. Describe what happens with baking soda, calcium chloride and phenol red are mixed.

5. What are evidences of chemical change?

6. Is this an endothermic or exothermic reaction? How do you know?

7. Give three examples of exothermic reactions in everyday life.

ELABORATE• Ice Ice Baby

– Baking soda and vinegar– Is this endothermic or exothermic? How do

you know?– Give 3 examples of everyday endothermic

reactions.

• Ice Cream– Are the changes physical or chemical?– Is the ice cream endothermic or exothermic?

How do you know?– Is the ice/salt mix endothermic or exothermic?

How do you know?

EVALUATION• Complete Type of Change? Endo/Exo

chart

• Complete graph analysis questions