Chemical Reactions Intro

Introduction to Chemical Reactions

What is a chemical reaction?

• A chemical reaction is when one or more substances undergoes a chemical change into a new substance(s).

• We represent chemical reactions with chemical equations.

We use letters to indicate the state a substance is in during a reaction.

Multiple Choice

A _____ is a chemical change when reactants change to become different products.

• chemical change

• chemical reaction

• chemical equation

• chemistry

Multiple Choice

What is the arrow in a chemical equation...

H_{2 +} O --> H₂O

• Reactants

• Products

• Yields

• Chemical Equation

Multiple Choice

The blue numbers in the image below represent ________

• I don't know, and don't want to try
• coefficients
• subscripts
• none of the answers are correct

Multiple Choice

The red numbers in the image below represent ________

• subscripts
• coefficients
• I don't know, and don't want to try
• None of the answers are correct

Multiple Choice

What is the part of the chemical equation in green called? 
Fe + S --> FeS

• products
• reactants
• yield
• chemical formula

Multiple Choice

When an italics lower case aq, (aq), is found beside a chemical in an equation it indicates that the chemical is _____________.

• liquid

• a precipitate in water

• dissolved in water

• gaseous

Multiple Choice

When an italics lower case g, (g), is found beside a chemical in an equation it indicates that the chemical is _____________.

• liquid

• insouble

• soluble

• gaseous

Multiple Choice

When an italics lower case s, (s), is found beside a chemical in an equation it indicates that the chemical is _____________.

• souble

• insouble

• solid

• silver

Indicators of a Chemical Reaction

• Formation of a gas

• Formation of a precipitate

• Change in color

• Change in temperature without heating or cooling it

• Production of light

• Production of an odor

Law of Conservation of Mass

• Matter is neither created nor destroyed, only changed.

• This means that the atoms used at the start of the reaction must equal the amount of atoms at the end of the reaction. Therefore, we must balance chemical equations.

Coefficients

In order to balance chemical equations, we use coefficients. Coefficients mutliply the number of atoms in a formula.

Multiple Choice

The coefficient in  3H₂O is

• 6
• 2
• 3
• 5

Multiple Choice

How many Hydrogen (H) atoms are in 4NH₃?

• 4

• 1

• 3

• 12

Multiple Choice

How many Nitrogen (N) atoms are in 4NH₃?

• 4

• 1

• 3

• 12

Multiple Choice

How many Al atoms are in this compound? 4Al₂O₃

• 2

• 8

• 6

• 4

Multiple Choice

How many atoms of oxygen are represented in 2Ca(NO₃)₂?

• 4
• 6
• 10
• 12

Multiple Choice

Matter can not be created nor destroyed: it can only be

• Destroyed a little bit

• Invisible

• Transformed, changed

• None of the above

Multiple Choice

If reaction starts with 20g of reactants it should produce

• a total of 40g of products

• a total of 10g of products

• a total of 80 g of products

• a total of 20g of products

Multiple Choice

You know you a chemical reaction has occurred if 

• there is a precipitate.
• there is a color change.
• there is a temperature change.
• All of these answers are evidence.