Chemical Reactions

Chemical Reactions

Open Ended

Think-Share:

What first comes to mind when you hear the words CHEMICAL REACTION?

(you have 1 minute)

How can you tell a chemical reaction is happening?

• A change of color occurs during the reaction

• A gas is produced during the reaction.

• A solid product called a precipitate is produced during the reaction.

• A transfer of energy occurs as a result of the reaction.

Example 1: Color Change

A solution of potassium permanganate is added to a solution of sodium hydroxide and sugar.

Notice how the colors change as the reaction continues 

Poll

When food coloring is added to water, is a chemical reaction taking place?

• Yes

• No

A chemical reaction is NOT taking place? WHY???

• Your reactants are food coloring and water and the product is food coloring and water.

• There were no other signs of a chemical reaction taking place

• The color change of water (went from clear to the color of the food coloring) was predictable.  Often the color change in a chemical reaction are not necessarily predictable (as in the video) 

Example 2: gas production

When zinc reacts with nitric acid, the reaction bubbles vigorously as Nitrogen gas is produced. The production of a gas is also an indication that a chemical reaction is occurring.

Example 3: precipitate formation

When a colorless solution of lead(II) nitrate is added to a colorless solution of potassium iodide, a yellow solid called a precipitate is instantly produced.

Transfer of Energy

• All chemical changes involve a transfer of energy. 

• Energy/heat can be absorbed =Endothermic reaction.

• Or

• Energy/heat can be given off=Exothermic reaction

Example 4: Energy Transfer

Sodium and water produce an explosion. Energy/heat is being released. This is an exothermic reaction.

Open Ended

In two minutes,

write the four indicators of a chemical change.

Multiple Choice

Which of the following describes changes in energy during a chemical reaction?

• Changes in energy do not occur during a chemical reaction.

• Energy is always released during a reaction.

• Energy may be either absorbed or released during a reaction.

• Energy is always released during a reaction.

Multiple Select

Which of the following indicated a chemical change/chemical reaction?

• Precipitate formation

• Transfer of heat energy

Open Ended

Two reactants are mixed in a test tube, and the test tube becomes very warm. This is a sign of a transfer of ______ taking place.

Multiple Select

What state of matters, when produced, is a sign that a chemical reaction is occuring?

• gas

• liquid

• solid

• plasma

Multiple Choice

When a color change happens, a chemical reaction must have occurred.

• false

• true

Poll

Lesson Reflection: How confident do you feel in your ability to determine if a chemical change has occurred?

• very confident

• confident

• partly confident

• not confident at all