PAGE 12 — Chemical Properties & PAGE 13 — Chemical Reactions & PAGE 14 — Reaction Types & PAGE 15 — More Reaction Types

What is a physical property?

A characteristic that can be observed or measured without changing the substance.

What is a chemical property?

A characteristic that describes a substance’s ability to undergo a chemical change.

Does observing a physical property change the substance?

No, the substance stays the same.

Does observing a chemical property change the substance?

Yes, it forms a new substance.

Do physical properties create a new substance?

No.

Examples of physical properties?

• Color

• Density

• Melting point

• Boiling point

• Mass

• Volume

• State of matter

• Solubility

• Conductivity

Examples of Chemical Properties?

• Flammability

• Reactivity with oxygen

• Ability to rust

• Ability to tarnish

• Reactivity with acids

• Ability to decompose

Do chemical properties create a new substance?

Yes a chemical change occurs.

Is melting a physical or chemical property?

Physical (state change only).

Is burning a physical or chemical property?

Chemical (new substances form).

Is rusting a physical or chemical property?

Chemical (iron → iron oxide).

Is density a physical or chemical property?

Physical.

Is reactivity a physical or chemical property?

Chemical

What is the purpose of balancing a chemical equation?

To make sure atoms are equal on both sides (law of conservation of mass).

What can you change when balancing an equation?

Coefficients (numbers in front of molecules).

What can you NOT change when balancing an equation?

Subscripts (numbers inside the formula).

What does the law of conservation of mass state?

Matter cannot be created or destroyed, only rearranged.

Balance: H₂ + O₂ → H₂O

2H₂ + O₂ → 2H₂O

Balance: N₂ + H₂ → NH₃

N₂ + 3H₂ → 2NH₃

Balance: CH₄ + O₂ → CO₂ + H₂O

CH₄ + 2O₂ → CO₂ + 2H₂O

What indicates a chemical reaction occurred?

New substances form.

What does a coefficient do?

Multiplies the entire molecule.

What does a subscript do?

Shows how many atoms are inside a molecule (cannot be changed).

What does the law of conservation of mass state?

Matter cannot be created or destroyed, only rearranged.

In a chemical reaction, how must the number of atoms compare on both sides?

They must be equal on both sides.

Why must chemical equations be balanced?

To obey the law of conservation of mass.

If 20 g of reactants are used, how much product must form?

20 g (mass in = mass out).

If 15 g of A reacts with 5 g of B, what is the total mass of products?

20 g.

If products total 12 g, what was the mass of reactants?

12 g.

What must be true for a chemical equation to follow conservation of mass?

Same number of each atom on both sides.

Does mass change during a chemical reaction?

No, total mass stays the same.

Does balancing equations change the actual reaction?

No, it only adjusts how many molecules are shown

What is a synthesis reaction?

A reaction where two or more substances combine to form one product.

What is the general formula for a synthesis reaction?

A + B → AB

Does the number of products increase or decrease in a synthesis reaction?

Decrease

• multiple reactants form one product.

Is a synthesis reaction the opposite of decomposition?

Yes

• synthesis builds, decomposition breaks down.

Synthesis (hydrogen + oxygen → water).

What type of reaction is: 2H₂ + O₂ → 2H₂O?

What must be true for the equation to follow conservation of mass?

Same number of atoms on both sides.

What keyword helps identify a synthesis reaction?

“Combine” or “form one product”

How many products does a synthesis reaction have?

One

What does a synthesis reaction do?

Builds a more complex substance.

What keyword helps identify a decomposition reaction?

“Breaks down” or “splits apart”.

How many reactants does a decomposition reaction have?

One

What does a decomposition reaction do?

Breaks a compound into simpler substances.

What is a decomposition reaction?

A reaction where one reactant breaks down into two or more products.

What is the general formula for a decomposition reaction?

AB → A + B

Does the number of products increase or decrease in a decomposition reaction?

Increase

• one reactant forms multiple products.

Is decomposition the opposite of synthesis?

Yes

• decomposition breaks apart, synthesis builds.

What keyword helps identify a single replacement reaction?

“Replaces” or “kicks out”

What must be true for a single replacement reaction to occur?

The free element must be more reactive than the one it replaces.

What does a single replacement reaction do?

Swaps one element in a compound with another.

What is a single replacement reaction?

A reaction where one element replaces another element in a compound.

What is the general formula for a single replacement reaction?

A + BC → AC + B

How many reactants are in a single replacement reaction?

Two

• one element and one compound.

How many products form?

Two

• a new compound and a displaced element.

What keyword helps identify a double replacement reaction?

“Swap ions” or “exchange partners”.

What must happen for a double replacement reaction to occur?

One product must be a solid (precipitate), gas, or water.

What does a double replacement reaction do?

Exchanges ions between two compounds.

What is a double replacement reaction?

A reaction where two compounds swap ions to form two new compounds.

What is the general formula for a double replacement reaction?

AB + CD → AD + CB

How many reactants are in a double replacement reaction?

Two compounds.

How many products form?

Two new compounds.

What keyword helps identify a combustion reaction?

“Burns” or “reacts with oxygen”

What must always be a reactant in a combustion reaction?

Oxygen (O₂)

What does a combustion reaction release?

Energy (heat and/or light)

What type of compounds usually undergo combustion?

Hydrocarbons (compounds made of C and H)

What is a combustion reaction?

A reaction where a substance reacts with oxygen (O₂) to produce carbon dioxide (CO₂) and water (H₂O).

What is the general formula for a combustion reaction?

Hydrocarbon + O₂ → CO₂ + H₂O

What are the typical products of combustion?

CO₂ and H₂O

What is activation energy?

The minimum amount of energy needed to start a chemical reaction.

Why is activation energy needed?

To break bonds in the reactants so new bonds can form.

What happens if molecules don’t have enough activation energy?

No reaction occurs

What does a catalyst do to activation energy?

Lowers activation energy.

What is the effect of lowering activation energy?

The reaction happens faster.

Does a catalyst get used up in a reaction?

No, it is not consumed.

Does activation energy affect the total energy released or absorbed?

No, only the speed of the reaction.

Do exothermic and endothermic reactions both require activation energy?

Yes, all reactions need it to begin.