Apply Chemical Properties and Reactions - GED Science

SECTION 1

Historical Context & Motivation

Humans have been using chemical reactions for thousands of years — from fermenting grapes into wine to smelting metal ores into tools. Yet for most of history, people did not understand why these transformations happened. It took centuries of careful observation, failed experiments, and brilliant breakthroughs before scientists developed the principles of chemistry that we rely on today.

~3000 BCE • Ancient Metallurgy

Early civilizations in Egypt and Mesopotamia smelted copper and tin ores to create bronze, performing chemical reactions long before the concept of chemistry existed.

1661 • Boyle Defines Elements

Robert Boyle published "The Sceptical Chymist," arguing that elements are fundamental substances that cannot be broken down further — a key step away from alchemy toward modern chemistry.

1789 • Lavoisier & Conservation of Mass

Antoine Lavoisier demonstrated that mass is conserved in chemical reactions. His careful measurements showed that nothing is created or destroyed — atoms simply rearrange.

1869 • Mendeleev's Periodic Table

Dmitri Mendeleev organized elements by their chemical properties and atomic mass, creating the periodic table. This tool predicted how elements would react with one another.

1916 • Lewis & Chemical Bonding

Gilbert Lewis proposed that atoms share or transfer electrons to form bonds, explaining why chemical reactions happen at the atomic level.

Understanding chemical properties and reactions is not just academic — it is central to everyday life. When you cook food, take medicine, clean your home, or start your car, chemical reactions are at work. On the GED Science test, you will be asked to read passages, examine data tables, and interpret diagrams that describe these reactions. The core question this lesson addresses is: How do we identify, classify, and predict the outcomes of chemical reactions?

SECTION 2

Core Principles & Definitions

Before diving into specific reaction types, you need to know the foundational ideas that govern all of chemistry. Every substance has two kinds of properties: physical properties (characteristics you can observe without changing the substance, like color, melting point, or density) and chemical properties (characteristics that describe how a substance reacts with other substances, like flammability, reactivity with acid, or tendency to rust). On the GED, you will need to distinguish between these two categories.

Chemical vs. Physical Change

A chemical change produces one or more new substances with different properties (burning wood, rusting iron). A physical change alters appearance but not composition (melting ice, cutting paper).

Reactants & Products

In a chemical equation, the starting substances are called reactants (written on the left side of the arrow). The new substances formed are called products (written on the right side).

Conservation of Mass

Atoms are never created or destroyed in a chemical reaction — they are rearranged. The total mass of the reactants always equals the total mass of the products.

Energy in Reactions

Every chemical reaction either absorbs energy (endothermic) or releases energy (exothermic). Burning fuel releases heat; photosynthesis absorbs light energy.

Balancing Equations

A balanced chemical equation has equal numbers of each type of atom on both sides of the arrow, reflecting the law of conservation of mass.

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KEY TAKEAWAY

Think of a chemical reaction like rearranging LEGO bricks. You start with a set of bricks assembled one way (reactants) and rebuild them into a completely different structure (products). No bricks are added or removed — they are just rearranged. That is the law of conservation of mass.

SECTION 3

Visual Explanation: Anatomy of a Chemical Equation

This diagram shows the combustion of methane. The reactants (CH₄ and 2O₂) appear on the left, the arrow means "yields," and the products (CO₂ and 2H₂O) appear on the right. The atom count is identical on both sides, confirming the equation is balanced.

When you see a chemical equation on the GED, read it like a sentence. The substances on the left are the reactants — the ingredients that go into the reaction. The arrow (→) means "produces" or "yields." The substances on the right are the products — the new substances that form. The numbers placed in front of each formula, called coefficients, tell you how many molecules of each substance are involved. The small numbers within a formula, called subscripts, tell you how many atoms of each element are in one molecule. Together, coefficients and subscripts allow you to count every atom and verify the equation is balanced.

SECTION 4

How Chemical Reactions Work

At the atomic level, chemical reactions involve the breaking and forming of chemical bonds — the forces that hold atoms together. Breaking bonds requires energy input, while forming new bonds releases energy. The overall energy change determines whether a reaction is exothermic (releases more energy than it absorbs) or endothermic (absorbs more energy than it releases).

Signs of a Chemical Reaction

On the GED, you may be asked to read a passage describing an experiment and determine whether a chemical reaction occurred. Look for these observable clues: a color change (e.g., a silver nail turning brown in copper sulfate solution), the formation of a gas (bubbles appearing), a temperature change (the container gets hot or cold), the formation of a precipitate (a solid forming in a liquid), or a new odor. These are not absolute proof, but they are strong indicators.

Conservation of Mass in Equations

LAW OF CONSERVATION OF MASS

Total mass of reactants = Total mass of products

In any closed system, the mass before a reaction equals the mass after the reaction. If you start with 16 g of methane and 64 g of oxygen (80 g total), you will end with exactly 80 g of products.

Balancing a Simple Equation

UNBALANCED EQUATION

H₂ + O₂ → H₂O

Left side: 2 H, 2 O. Right side: 2 H, 1 O. The oxygen atoms are not equal — this equation is unbalanced.

BALANCED EQUATION

2H₂ + O₂ → 2H₂O

Left side: 4 H, 2 O. Right side: 4 H, 2 O. Now every atom is accounted for. We balanced it by placing coefficients (the large "2" in front of H₂ and H₂O).

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GED TIP

On the GED, you will rarely be asked to balance an equation from scratch. Instead, you will be given an equation and asked to verify whether it is balanced, identify what the coefficients mean, or use it to determine the ratio of reactants to products.

SECTION 5

Types of Chemical Reactions

Chemists classify reactions into several major categories. On the GED, you may see a passage describing a reaction and be asked to identify its type, or you may need to predict what products form. The five most common types are synthesis, decomposition, single replacement, double replacement, and combustion. The diagram below provides a visual overview.

The five major reaction types are shown with their general patterns and real-world examples. Notice how synthesis and decomposition are essentially opposites: one combines substances, the other breaks them apart.

Reaction Type	General Pattern	Quick Identifier
Synthesis	A + B → AB	Two or more reactants form one product
Decomposition	AB → A + B	One reactant breaks into two or more products
Single Replacement	A + BC → AC + B	A lone element swaps with part of a compound
Double Replacement	AB + CD → AD + CB	Two compounds exchange partners
Combustion	Fuel + O₂ → CO₂ + H₂O	Oxygen is always a reactant; produces CO₂ and H₂O

Summary of the five major chemical reaction types

SECTION 6

Worked Example: Identifying and Balancing a Reaction

Let's walk through a GED-style problem step by step. Suppose you are given the following unbalanced equation and asked to balance it and identify the reaction type:

UNBALANCED EQUATION

Fe + O₂ → Fe₂O₃

Iron reacts with oxygen gas to form iron(III) oxide (rust).

Balancing and Classifying the Reaction

1
Step 1 — Count Atoms on Each Side (Unbalanced)

Left side: 1 Fe, 2 O. Right side: 2 Fe, 3 O. Neither iron nor oxygen is balanced.

Not balanced — Fe and O counts differ across the arrow.
2
Step 2 — Balance Iron First

There are 2 Fe on the right, so place a coefficient of 4 in front of Fe on the left. Wait — let's start by finding the least common multiple for oxygen. The left has O₂ (groups of 2) and the right has O₃ (groups of 3). The LCM of 2 and 3 is 6. So we need 3 O₂ on the left (giving 6 O atoms) and 2 Fe₂O₃ on the right (giving 6 O atoms).

Intermediate equation: Fe + 3O₂ → 2Fe₂O₃
3
Step 3 — Balance Iron to Match

Now the right side has 2 × 2 = 4 Fe atoms. Place a 4 in front of Fe on the left.

Balanced equation: 4Fe + 3O₂ → 2Fe₂O₃
4
Step 4 — Verify the Count

Left side: 4 Fe, 6 O (3 × 2). Right side: 4 Fe (2 × 2), 6 O (2 × 3). Both sides match.

✓ Balanced — Conservation of mass confirmed.
5
Step 5 — Identify the Reaction Type

Two reactants (Fe and O₂) combine to form one product (Fe₂O₃). This fits the pattern A + B → AB.

This is a synthesis (combination) reaction.

SECTION 7

Exothermic vs. Endothermic Reactions

The GED frequently tests whether you can distinguish between reactions that release energy and reactions that absorb energy. These categories — exothermic and endothermic — are among the most commonly tested concepts in physical science. Understanding them is essential for interpreting graphs, experimental data, and passages about energy transfer.

Feature	Exothermic	Endothermic
Energy direction	Energy is released to the surroundings	Energy is absorbed from the surroundings
Temperature effect	Surroundings get warmer	Surroundings get cooler
Energy of products vs. reactants	Products have less energy than reactants	Products have more energy than reactants
Everyday examples	Burning wood, hand warmers, rusting	Photosynthesis, melting ice, cold packs
On an energy diagram	Products are lower than reactants	Products are higher than reactants

Comparison of exothermic and endothermic reactions

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KEY TAKEAWAY

Think of energy in a reaction like money in a transaction. In an exothermic reaction, the reaction "pays out" energy to its surroundings — you feel warmth. In an endothermic reaction, the reaction "charges" the surroundings — it takes energy in, and you feel cold. The prefix "exo" means out; "endo" means in.

SECTION 8

Connections to Broader Science

Chemical reactions do not exist in isolation — they connect to nearly every branch of science tested on the GED. In life science, chemical reactions power living organisms through processes like photosynthesis and cellular respiration. In earth science, chemical reactions drive rock weathering and the formation of fossil fuels. On the GED, a question might connect a chemical concept to one of these broader topics.

Basic GED Concept	Advanced Connection	Why It Matters
Balancing equations (conservation of mass)	Stoichiometry — predicting exact amounts of products	Industry uses stoichiometry to calculate how much raw material is needed
Exothermic / endothermic	Thermodynamics — energy transfer in complex systems	Understanding climate science, engine efficiency, and metabolism
Reaction types (synthesis, decomposition, etc.)	Organic chemistry — reactions of carbon-based molecules	Drug development, plastics, and biological chemistry all depend on reaction types
Combustion	Environmental science — greenhouse gases and climate change	Burning fossil fuels is a combustion reaction that produces CO₂

How GED-level chemistry concepts connect to more advanced science

You do not need to master these advanced topics for the GED, but knowing that these connections exist can help you answer cross-disciplinary questions. For example, a GED passage might describe how burning coal (a combustion reaction) contributes to increased CO₂ in the atmosphere. Understanding that combustion produces CO₂ gives you the foundation to answer that question confidently.

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LOOKING AHEAD

If you continue studying science after the GED, you will encounter reaction rates (how fast reactions happen), equilibrium (when forward and reverse reactions balance), and acid-base chemistry. All of these build directly on the reaction concepts covered in this lesson.

SECTION 9

Practice Problems

Question 1: CONCEPTUAL

A student mixes baking soda and vinegar in a beaker. She observes bubbling, a temperature drop, and the formation of a gas. Her lab partner argues that this is a physical change because the substances are still liquids. Which of the following best explains why the student's observation indicates a chemical change rather than a physical change?

A. The liquid changed color from clear to slightly cloudy.
B. A new gaseous substance (CO₂) was produced, which was not present before the mixing.
C. The volume of liquid in the beaker decreased due to evaporation.
D. The mixture could be separated back into baking soda and vinegar by filtering.

Show answer (B)

B is correct. The formation of a new substance — carbon dioxide gas (CO₂) — that was not present before the reaction is strong evidence of a chemical change. New substances with different chemical properties are produced. A is incorrect because color changes alone can occur in physical changes (like dissolving a dye). C is incorrect because evaporation is a physical change, not evidence of a chemical reaction. D is incorrect because if the original substances could be recovered by simple separation, it would suggest a physical change, not a chemical one — and in fact, you cannot recover the original baking soda and vinegar from the products.

Question 2: BASIC CALCULATION

Consider the following balanced equation: 2H₂ + O₂ → 2H₂O A chemist starts with 10 grams of hydrogen gas (H₂) and 80 grams of oxygen gas (O₂). According to the law of conservation of mass, what is the total mass of the water (H₂O) produced?

A. 70 grams
B. 80 grams
C. 90 grams
D. 100 grams

Show answer (C)

C is correct. By the law of conservation of mass, the total mass of reactants must equal the total mass of products. The reactants total 10 g + 80 g = 90 g, so the products must also total 90 g. Since water is the only product, the mass of water produced is 90 grams. A (70 g) is wrong because it subtracts instead of adding. B (80 g) only accounts for the oxygen mass. D (100 g) incorrectly adds extra mass that does not exist in the system.

Question 3: INTERMEDIATE

A scientist tests four different reactions in the lab and records the following observations: Reaction 1: Zinc metal is placed into a copper sulfate solution. The zinc dissolves and copper metal appears on the zinc's surface. Reaction 2: Hydrogen peroxide slowly breaks down into water and oxygen gas. Reaction 3: Methane gas burns in air, producing carbon dioxide and water vapor. Reaction 4: Solutions of sodium chloride and silver nitrate are mixed, forming a white solid (silver chloride) and sodium nitrate in solution. Which reaction is an example of a single replacement reaction?

A. Reaction 1
B. Reaction 2
C. Reaction 3
D. Reaction 4

Show answer (A)

A is correct. In Reaction 1, zinc (a lone element) replaces copper in the compound copper sulfate: Zn + CuSO₄ → ZnSO₄ + Cu. This matches the single replacement pattern (A + BC → AC + B). B is incorrect because Reaction 2 is a decomposition reaction (one substance breaks into two: H₂O₂ → H₂O + O₂). C is incorrect because Reaction 3 is a combustion reaction (fuel + O₂ → CO₂ + H₂O). D is incorrect because Reaction 4 is a double replacement reaction (two compounds exchange partners: NaCl + AgNO₃ → AgCl + NaNO₃).

Question 4: APPLIED

2 pts

A student conducts an experiment to determine whether a reaction is exothermic or endothermic. She dissolves ammonium nitrate in water inside a beaker and records the temperature every 30 seconds. Her data are shown below: Time (seconds): 0 | 30 | 60 | 90 | 120 Temperature (°C): 22.0 | 18.5 | 15.2 | 13.8 | 13.5 Based on the data, is the dissolving of ammonium nitrate exothermic or endothermic? Explain how the data support your conclusion. Include at least one piece of evidence from the data and connect it to the definition of the reaction type. (Write 3–7 sentences.)

Show answer

Rubric (2 points): Point 1 (Correct identification with definition): The student correctly identifies the reaction as endothermic AND explains that an endothermic reaction absorbs energy from the surroundings, causing the temperature to decrease. Example: "The dissolving of ammonium nitrate is endothermic because the process absorbs heat energy from the water." Point 2 (Evidence from data): The student cites specific data to support the conclusion. Example: "The temperature dropped from 22.0°C at the start to 13.5°C after 120 seconds, a decrease of 8.5°C. This temperature drop in the surroundings (the water) is evidence that the reaction absorbed thermal energy from the water." Sample full-credit response: "The dissolving of ammonium nitrate in water is an endothermic process. An endothermic reaction absorbs energy from its surroundings, which causes the surrounding temperature to drop. The data clearly support this conclusion: the temperature fell from 22.0°C at the start to 13.5°C after two minutes — a decrease of 8.5°C. If the reaction were exothermic, the temperature would have increased instead. The consistent downward trend in the data confirms that energy was being pulled from the water into the dissolving process."

Question 5: CRITICAL THINKING

3 pts

A research team investigates how temperature affects the rate of a decomposition reaction. They place identical samples of hydrogen peroxide (H₂O₂) in water baths at different temperatures and measure the volume of oxygen gas (O₂) produced over 5 minutes. Their data are below: Trial | Water Bath Temp (°C) | O₂ Produced (mL) in 5 min 1 | 10 | 8 2 | 25 | 22 3 | 40 | 51 4 | 55 | 105 5 | 70 | 198 Using the data, describe the relationship between temperature and reaction rate. Then evaluate the experimental design: identify the independent variable, the dependent variable, and one variable the team should have controlled. Finally, explain why the trend in the data makes sense based on what happens to particles at higher temperatures. (Write 5–7 sentences.)

Show answer

Rubric (3 points): Point 1 (Data relationship): The student correctly describes that as temperature increases, the volume of O₂ produced increases, meaning the reaction rate increases with temperature. Specific data should be cited: for example, at 10°C only 8 mL of O₂ was produced, but at 70°C the amount jumped to 198 mL. Point 2 (Experimental design analysis): The student correctly identifies the independent variable (water bath temperature), the dependent variable (volume of O₂ gas produced), and at least one controlled variable (e.g., the amount/concentration of H₂O₂, the time allowed for each trial, the volume of solution, or the type of container used). Point 3 (Particle-level explanation): The student explains that at higher temperatures, particles move faster and collide more frequently and with greater energy, which increases the rate at which H₂O₂ molecules decompose into H₂O and O₂. Sample full-credit response: "The data show a clear positive relationship between temperature and reaction rate. At 10°C, only 8 mL of oxygen was produced in 5 minutes, while at 70°C the volume increased dramatically to 198 mL. The independent variable is the water bath temperature, the dependent variable is the volume of O₂ gas collected, and one variable that should be controlled is the concentration of the hydrogen peroxide solution — if different trials used different concentrations, the results would be unreliable. The trend makes sense at the particle level because higher temperatures cause molecules to move faster. Faster-moving molecules collide more often and with greater force, so bonds in H₂O₂ break more readily, producing O₂ at a faster rate. This is consistent with the general principle that increasing temperature increases reaction rate."

SUMMARY

Lesson Summary

Summary

Chemical reactions involve the rearrangement of atoms to form new substances. Every substance has chemical properties that describe how it interacts with other substances, as opposed to physical properties that can be observed without changing composition. In a chemical equation, reactants appear on the left and products appear on the right, connected by an arrow. The law of conservation of mass requires that atom counts be equal on both sides — this is why we balance equations using coefficients.

The five major reaction types are synthesis (A + B → AB), decomposition (AB → A + B), single replacement, double replacement, and combustion (fuel + O₂ → CO₂ + H₂O). Reactions are also classified by energy flow: exothermic reactions release heat and warm the surroundings, while endothermic reactions absorb heat and cool the surroundings. On the GED, focus on reading stimulus materials carefully, identifying reaction types from descriptions, applying conservation of mass, and interpreting data about energy changes.