GED Prep: Physical Science (Atoms, Chemical Reactions, Forces, Energy, Waves)

GED – Physical Science (Atoms, Chemical Reactions, Forces, Energy, Waves)

GED Physical Science Study Guide: Atoms, Chemical Reactions, Forces, Energy, and Waves

What This Is

Physical Science on the GED tests your understanding of fundamental concepts like atomic structure, chemical reactions, forces, energy transformations, and wave properties. These topics appear in multiple-choice, drag-and-drop, and short-answer questions, often requiring you to interpret diagrams, graphs, or real-world scenarios. For example, you might be asked: "A student mixes baking soda (NaHCO₃) and vinegar (CH₃COOH), producing carbon dioxide gas. What type of reaction is this?" This guide will help you break down key terms, avoid common mistakes, and apply strategies to solve these questions efficiently.

Key Terms & Rules

Atoms & the Periodic Table

• Atom: The smallest unit of an element, made of protons (+), neutrons (0), and electrons (–).
• Atomic Number: Number of protons in an atom (defines the element). Example: Carbon (C) has atomic number 6.
• Mass Number: Protons + neutrons. Example: Carbon-12 has 6 protons and 6 neutrons.
• Isotopes: Atoms of the same element with different numbers of neutrons (same atomic number, different mass number).
• Periodic Table Groups: Columns (vertical) share similar chemical properties. Example: Group 1 (alkali metals) are highly reactive.
• Periodic Table Periods: Rows (horizontal) show increasing atomic number.

Chemical Reactions

• Chemical Equation: Shows reactants → products. Example: 2H₂ + O₂ → 2H₂O (balanced equation).
• Balanced Equation: Same number of each atom on both sides (conservation of mass).
• Types of Reactions:
• Synthesis: A + B → AB (Example: 2H₂ + O₂ → 2H₂O)
• Decomposition: AB → A + B (Example: 2H₂O → 2H₂ + O₂)
• Single Replacement: A + BC → AC + B (Example: Zn + 2HCl → ZnCl₂ + H₂)
• Double Replacement: AB + CD → AD + CB (Example: AgNO₃ + NaCl → AgCl + NaNO₃)
• Combustion: Hydrocarbon + O₂ → CO₂ + H₂O (Example: CH₄ + 2O₂ → CO₂ + 2H₂O)

Forces & Motion

• Newton’s Laws of Motion:
• Inertia: Objects in motion stay in motion unless acted on by an unbalanced force.
• F = ma: Force = mass × acceleration. Example: A 5 kg object accelerating at 2 m/s² has a force of 10 N.
• Action-Reaction: For every action, there’s an equal and opposite reaction.
• Gravity: Force pulling objects toward each other (F = G × (m₁m₂)/r²).
• Friction: Force opposing motion (static vs. kinetic friction).

Energy

• Kinetic Energy (KE): Energy of motion. Formula: KE = ½mv²
• Potential Energy (PE): Stored energy (gravitational, chemical, elastic). Formula: PE = mgh (gravitational)
• Law of Conservation of Energy: Energy cannot be created or destroyed, only transformed.
• Energy Transformations: Example: A battery (chemical PE) → flashlight (electrical KE) → light (radiant energy).

Waves

• Wavelength (λ): Distance between wave crests.
• Frequency (f): Number of waves per second (Hz). Formula: v = λf (wave speed = wavelength × frequency).
• Types of Waves:
• Mechanical Waves: Require a medium (sound, ocean waves).
• Electromagnetic Waves: Do not require a medium (light, radio waves).
• Wave Behaviors:
• Reflection: Bouncing back (mirror).
• Refraction: Bending when changing medium (straw in water).
• Diffraction: Spreading around obstacles (sound around a corner).

Step-by-Step / Process Flow

How to Solve a Chemical Reaction Question

1. Identify the type of reaction (synthesis, decomposition, etc.) by looking at reactants/products.
2. Example: If a single element replaces another in a compound, it’s single replacement.
3. Check if the equation is balanced (count atoms on both sides).
4. Example: H₂ + O₂ → H₂O is unbalanced (2 O on left, 1 on right).
5. Balance the equation by adding coefficients (never change subscripts!).
6. Example: 2H₂ + O₂ → 2H₂O (now balanced).
7. Eliminate answer choices that don’t match the reaction type or balanced equation.
8. Plug in real-world context if given (e.g., "This reaction produces heat → likely combustion").

How to Solve a Force/Motion Problem

1. Read the question carefully – is it asking for force, acceleration, or mass?
2. List known values (e.g., mass = 10 kg, acceleration = 3 m/s²).
3. Choose the correct formula (F = ma, KE = ½mv², etc.).
4. Plug in numbers and solve (use a calculator if allowed).
5. Check units (force in Newtons (N), energy in Joules (J)).

How to Analyze a Wave Graph

1. Identify the wave type (mechanical vs. electromagnetic).
2. Find wavelength (λ) by measuring distance between two crests.
3. Find amplitude (height from rest to crest).
4. Calculate frequency (f) if wave speed (v) is given (v = λf).
5. Match to answer choices (e.g., "Which wave has the highest frequency?").

Common Mistakes

Exam Insights

1. Most-Tested Concepts:
2. Balancing chemical equations (especially combustion and single replacement).
3. Newton’s 2nd Law (F = ma) and energy transformations (PE → KE).
4. Wave properties (frequency, wavelength, speed).
5. Tricky Distinctions:
6. Isotopes vs. ions: Isotopes differ in neutrons; ions differ in electrons.
7. Speed vs. velocity: Velocity includes direction (vector); speed does not (scalar).
8. Common Distractors:
9. Unbalanced equations in answer choices.
10. Incorrect units (e.g., force in kg instead of N).
11. Mislabeling wave types (e.g., calling light a mechanical wave).
12. Calculator Tip: Use it for F = ma or KE = ½mv², but memorize basic formulas (e.g., v = λf).

Quick Check Questions

Question 1

A student drops a 2 kg ball from a height of 5 m. What is its potential energy just before it’s dropped? (Use g = 9.8 m/s²) A) 10 J B) 98 J C) 49 J D) 19.6 J

Answer: B) 98 J Explanation: PE = mgh = (2 kg)(9.8 m/s²)(5 m) = 98 J.

Question 2

Which of these is a decomposition reaction? A) 2H₂ + O₂ → 2H₂O B) 2H₂O → 2H₂ + O₂ C) Zn + 2HCl → ZnCl₂ + H₂ D) AgNO₃ + NaCl → AgCl + NaNO₃

Answer: B) 2H₂O → 2H₂ + O₂ Explanation: Decomposition breaks a compound into simpler substances.

Question 3

A wave has a wavelength of 4 m and a frequency of 3 Hz. What is its speed? A) 12 m/s B) 7 m/s C) 1 m/s D) 0.75 m/s

Answer: A) 12 m/s Explanation: v = λf = (4 m)(3 Hz) = 12 m/s.

Last-Minute Cram Sheet

1. Atoms: Protons = atomic number; mass number = protons + neutrons.
2. Balancing equations: Same number of atoms on both sides (coefficients only!).
3. F = ma: Force = mass × acceleration (units: N = kg·m/s²).
4. KE = ½mv², PE = mgh: Energy formulas (Joules).
5. v = λf: Wave speed = wavelength × frequency.
6. Combustion always produces CO₂ + H₂O.
7. ⚠️ Isotopes ≠ ions: Isotopes differ in neutrons; ions differ in electrons.
8. ⚠️ Velocity ≠ speed: Velocity includes direction.
9. ⚠️ Light is an electromagnetic wave (no medium needed).
10. ⚠️ GED loves energy transformations (PE → KE → thermal, etc.).