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1

Chemical Reactions

Processes by which atoms of one or more substances rearrange to form new substance(s) (represented by chemical equations).

2

Evidence of Reactions

1. Temperature Change
• exothermic - energy released (hot)
• endothermic - energy absorbed (cold)

2. Change of State
• formation of precipitate - solid formed when two aqueous solutions react
• gas release (bubbling, effervescence)
• disappearance of a solid

3. Smell

4. Colour Change
• transparent, translucent, opaque

5. Other Energy Changes: Light, Sound, Electrical

3

Parts of Chemical Equations

• reactants (left side)
• products (right side)
• arrow symbol (yields or produces)
• state symbols (s, l, g, or aq subscripts)
• Stoichiometric coefficients

4

Types of Equations

1. Word Equation: Uses names of substances

2. Skeleton Equation: Uses formulas of substances (HOFBrINCl -g, g, g, l, s, g, g, are diatomic molecules with the subscript 2)

3. Balanced Equation: Uses coefficients in front of formulas to make atoms equal on both sides

5

Law of Conservation of Mass

In any chemical reaction, the mass of the reactant(s) is equal to the mass of the product(s) (balanced).

6

Synthesis

More than one reactant, one product formed.

A + B -> C

A and B are compounds or elements, C is always a compound.

Metal oxide (s) + Water (l) -> Metal Hydroxide (Base)

Nonmetal oxide (g) + Water (l) -> Acid

7

Decomposition

One reactant, more than one product formed.

A -> B + C

A is always a compound, B and C are compounds or elements.

8

Single Displacement (Cation Single Displacement)

An element on the Activity Series replaces another below it (ionic compound + element on Activity Series).

AX + B -> BX + A

If B is not higher than A on the Activity series, there is no reaction.

9

Single Displacement (Anion Single Displacement)

A halogen replaces another below it (ionic compound + halogen)

AX + Y -> AY + X

10

Double Displacement (Neutralization)

Two ionic compounds switch ions
Acid + Base -> Salt + Water
AX + BY -> BX + AY

11

Double Displacement (Gas Releasing Double Displacement)

An acid or base reacts with a salt to form an acid or base that decomposes into water and the corresponding gas.

12

Double Displacement (Precipitation)

A solid is formed when two aqueous solutions react
AX (aq) + BY (aq) -> BX + AY
Use solubility chart to predict precipitate (one must be solid or no reaction)