2.3� Literacy Strategies: Using Base Words and
Comparing/Contrasting
Base Words:
Exo- means “out” → Exothermic: Energy goes out.
Endo- means “in” → Endothermic: Energy goes in.
Feature
Endothermic Reaction
Exothermic Reaction
Definition
Absorbs energy (usually
heat) from the
surroundings
Releases energy (usually
heat or light) to
surroundings
Energy Flow
Energy goes into the
system
Energy goes out of the
system
Temperature
Change
Surrounding temperature
decreases
Surrounding temperature
increases
ΔH (Enthalpy
Change)
Positive (ΔH > 0)
Negative (ΔH < 0)
Energy Level
Diagram
Products have more energy
than reactants
Products have less energy
than reactants
Examples
Photosynthesis, cooking an Combustion, respiration,
egg, melting ice
freezing water
Bond Behavior
More energy used to break
bonds
More energy released when
bonds form
Feels Like (if
Cold to the touch
touched)
Warm or hot to the touch
Real-Life Use
Hand warmers, burning
fuels
Cold packs, baking
⚗� Processing Chemical and Physical Changes
Chemical Change:
New substances are formed.
Signs: Color change, gas production, heat/light, precipitate.
Example: Rusting of iron.
Physical Change:
No new substances formed.
Example: Melting ice, dissolving sugar.
� Processing & Analyzing: Representing Energy Changes
Use Energy Level Diagrams to show differences in energy:
Exothermic Diagram: Reactants high, products low. Energy is released.
Endothermic Diagram: Reactants low, products high. Energy is
absorbed.
� Analyzing & Evaluating: Reading Energy Level Diagrams
Activation Energy: Minimum energy needed to start a reaction (shown as a
"hump" in diagram).
ΔH (Change in Enthalpy):
Negative ΔH = Exothermic
Positive ΔH = Endothermic
� Applying: Measuring Energy Changes
Use a calorimeter to measure temperature change of water when a
chemical reacts.
Formula: Q = mcΔT
Q = energy change (Joules)
m = mass of water (g)
c = specific heat capacity (usually 4.18 J/g°C)
ΔT = change in temperature (°C)
⚛� Chemistry 2.4: How Do Atoms Rearrange in
Different Types of Chemical Reactions?
� Literacy Strategies: Types of Chemical Reactions
Use acronyms like S.D.C.S.C. to remember:
Synthesis (S) – Two or more substances form one compound
A + B → AB
Example: 2H₂ + O₂ → 2H₂O
Decomposition (D) – One compound breaks into simpler substances
AB → A + B
Example: 2H₂O → 2H₂ + O₂
Combustion (C) – Hydrocarbon reacts with oxygen, produces CO₂ + H₂O
Example: CH₄ + 2O₂ → CO₂ + 2H₂O
Single Displacement (S) – One element replaces another
A + BC → AC + B
Example: Zn + CuSO₄ → ZnSO₄ + Cu
Double Displacement (C) – Ions in compounds switch places
AB + CD → AD + CB
Example: AgNO₃ + NaCl → AgCl + NaNO₃
� Processing & Communicating: Classifying Chemical Reactions
Look at the reactants and products to determine the type.
Practice writing balanced chemical equations to fully understand atom
rearrangement.
� Applying: Predicting Products
Predicting Reaction Types:
Use ion swapping for double displacement.
Check activity series to predict displacement reactions.
Apply combustion formulas for hydrocarbons (CxHy + O₂ → CO₂ + H₂O)
� Analyzing: Acids, Bases, and Salts
Acids:
pH less than 7
Taste sour, turn blue litmus red
Example: HCl, H₂SO₄
Bases:
pH greater than 7
Taste bitter, turn red litmus blue
Example: NaOH, NH₄OH
Neutralization Reaction:
Acid + Base → Salt + Water
Example: HCl + NaOH → NaCl + H₂O
� Applying: pH Scale
pH scale ranges from 0 to 14:
0–6: Acidic
7: Neutral
8–14: Basic
Strong acids have low pH, strong bases have high pH.
� Analyzing & Applying: pH Indicators
Litmus Paper:

Blue turns red = acid

Red turns blue = base
Universal Indicator:
Changes color depending on exact pH (rainbow scale)
Phenolphthalein:
Colorless in acid, pink in base