Chapter 23 – Chemical Reactions

23.1 – Chemical Changes

Objectives

• Identify the reactants and products in a chemical reaction.

• Determine how a chemical reaction satisfies the law of the conservation of matter.

• Determine how chemists express chemical changes using equations

Chemical Reactions

• change one or more substances into new substances– Reactants are substances combine or

change

– New substances that are produced are called Products

Different Reactions

• Chemical reactions – use the ELECTRONS to form new substances

• Nuclear reactions - use the NUCLEUS to form new substances

• What does a chemical reaction look like?

Think about it…

• If you burned a piece of paper, you end up with a pile of ashes.

• Once burned, is there…– More mass?– Same mass?– Less mass?

• Why?

Conservation of Mass

• Law that states, in a chemical reaction, matter is not created or destroyed, but stays the same.– Antoine Lavoisier experimented

with mercury (II) oxide and heat– He found mass of products (liquid

mercury and oxygen gas) equaled mass of reactants

Chemical Equation

• Uses chemical formulas and symbols to describe a chemical reaction and the product(s) it produces– Chemical formula expresses the

relationship between elements in the compound and molecules they make up

Chemical Equation

Reactants (left) → Products (right)

Arrow means “yields”

SnO2(s) + 2 H2(g) → Sn(s) + 2 H2O(g)

CH4(g) + 2 O2

(g) → CO2(g) + 2 H2O(g)

Coefficients

• Numbers which represent the number of units of each substance in a reaction– Knowing coefficients of chemical

reactions allows chemists to use the correct amount of reactants to predict the amount of products (law of conservation applies)

Example

Writing equations

• Subscripts are numbers which represent the number of atoms in a molecule of a particular element

• Symbols used to show state of reactants

– (s) solids– (aq) aqueous– (g) gas– (l) liquid

Volcano with a Twist

• Reactants?

• Products?

• Equation:

NaHCO3 ( ) + CH3COOH ( )

CH3COO-Na+ ( ) + H2O ( ) + CO2 ( )

• States?

• Conservation?

Exit slip on BR paper

• SnO2(s) + 2 H2(g) → Sn(s) + 2 H2O(g)

1.What are the reactants?

2.What are the products?

3.How is matter conserved?

In-class Assignment/Homework

• 23.1 WKT