Discover Chemical Properties: Reactivity, pH, and Combustibility

A chemical property describes how a substance can change into a completely new substance through a chemical reaction. Unlike physical properties such as color, shape, or size chemical properties only show up when a substance actually reacts and transforms into something different.

For example, when wood burns, it turns into ash and smoke. That ability to burn is a chemical property. You can connect this idea to what you already know about Physical Properties like mass, volume, and density, which describe a substance without changing what it is made of.

Reactivity is a chemical property that describes how easily a substance combines with another substance to form something new. A highly reactive substance reacts quickly and dramatically, while a substance with low reactivity barely reacts at all.

A great example is iron rusting. When iron is left outside in rain, it reacts with oxygen and water to form rust an orange, flaky new substance. This shows iron's reactivity. On the other hand, gold has very low reactivity, which is why it stays shiny and does not rust even after many years outdoors.

Another dramatic example is sodium metal, which reacts explosively when it touches water one of the most reactive substances you can study. When baking soda and vinegar are mixed, they also react and produce carbon dioxide gas bubbles, demonstrating reactivity between an acid and a base.

Combustibility describes a material's ability to catch fire and burn. When a material burns, it reacts with oxygen and releases heat and light energy, forming new substances like ash, smoke, and carbon dioxide. This makes combustion a chemical change, not a physical one.

Dry paper and wood are highly combustible they catch fire easily. Rocks, glass, and steel nails are not combustible at all. Gasoline is considered highly combustible, which is why it must be stored carefully away from flames. Knowing whether a material is combustible helps you stay safe by keeping it away from heat and fire sources.

Firefighters use water to cool burning materials and remove the heat needed for combustion to continue a real-world application of understanding this chemical property.

The pH scale measures how acidic or basic a liquid substance is, using numbers from 0 to 14. A pH of exactly 7 means the substance is neutral neither acidic nor basic. Pure water is a perfect example of a neutral substance.

Numbers below 7 indicate an acid. The lower the number, the stronger the acid. Lemon juice, vinegar, stomach acid (pH of 1), and orange juice are all acids. Acids often taste sour and can react with metals like iron.

Numbers above 7 indicate a base. Soapy water, baking soda dissolved in water, and bleach are all bases. Bases often feel slippery and are used in cleaning products.

You can measure pH using litmus paper, which changes color depending on whether a substance is an acid or a base. Red litmus paper turns blue in a base, and stays red in an acid. A pH meter is another tool scientists use to measure pH accurately.

Chemical Property: A chemical property is a characteristic that describes how a substance changes into a completely new substance through a chemical reaction. For example, the ability of wood to burn is a chemical property.

Reactivity: Reactivity is the ability of a substance to combine with another substance and form something new. A highly reactive substance, like sodium, reacts quickly and dramatically. A substance with low reactivity, like gold, barely reacts at all.

Combustibility: Combustibility describes a material's ability to catch fire and burn. When a material burns, it reacts with oxygen and creates new substances like ash and smoke. Dry paper and wood are highly combustible materials.

pH Scale: The pH scale is a numbered scale from 0 to 14 that measures how acidic or basic a liquid substance is. A pH of 7 is neutral, below 7 is acidic, and above 7 is basic.

Acid: An acid is a substance with a pH below 7. Acids often taste sour and can react with metals. Examples include lemon juice, vinegar, and stomach acid.

Base: A base is a substance with a pH above 7. Bases often feel slippery and are used in cleaning products. Examples include baking soda, soap, and soapy water.

Neutral: A neutral substance has a pH of exactly 7 it is neither an acid nor a base. Pure water is the most common example of a neutral substance.

Litmus Paper: Litmus paper is a special paper used to test whether a substance is an acid or a base. It turns red in acids and blue in bases, making it a useful pH measurement tool.

Combustion: Combustion is a chemical reaction where a material burns by reacting with oxygen, producing heat and light energy and forming new substances like ash and carbon dioxide.

Chemical Reaction: A chemical reaction is a process where substances interact and change into completely new substances. Burning, rusting, and fizzing between baking soda and vinegar are all examples of chemical reactions.

You can observe chemical properties through simple, safe tests. Mixing baking soda with vinegar produces bubbles of carbon dioxide gas this demonstrates reactivity between an acid and a base. Dipping litmus paper into lemon juice turns it red, showing the juice is acidic.

You can also think about everyday examples: a campfire burning wood shows combustibility, an iron nail turning orange and rough after being left outside shows reactivity with oxygen and water, and gold jewelry staying shiny for years shows very low reactivity.

Understanding these properties connects to Data Collection using quantitative and qualitative data and Experimental Design with multiple variables and controls, because scientists use careful tests and observations to identify chemical properties.

Before exploring chemical properties, it helps to understand the properties of rocks and minerals. In Rocks and Minerals Properties and Classification, you learned how scientists describe and sort materials based on their characteristics. Chemical properties are another layer of description that goes deeper than appearance.

You also build on your understanding of Particle Theory Arrangement and Movement of Particles, which explains why substances behave differently at the particle level during chemical reactions. Your knowledge of Phase Changes and Temperature Effects on State also helps you distinguish between physical changes and chemical changes.

This topic connects to many other important science ideas. Here is how they all fit together:

Physical Properties Mass, Volume, and Density is closely related because you need to understand the difference between physical and chemical properties. Physical properties describe a substance without changing it, while chemical properties describe how it reacts and transforms.

Phase Changes Temperature Effects on State connects because melting, freezing, and boiling are physical changes, not chemical ones an important distinction you will use when comparing property types.

Particle Theory Arrangement and Movement of Particles helps you understand why chemical reactions happen at the particle level when substances combine and form new materials.

Materials Science Properties and Applications builds directly on chemical properties, showing you how scientists choose materials based on their reactivity, combustibility, and pH for real-world uses.

Energy Conversion Transformations Between Forms connects to combustion, because burning releases chemical energy as heat and light a key energy transformation.

Experimental Design Multiple Variables and Controls and Data Collection Quantitative and Qualitative Data are the science skills you use to test and measure chemical properties safely and accurately.

Analysis Methods Patterns, Trends, and Relationships helps you make sense of the results when you test chemical properties and look for patterns in how substances react.

This topic prepares you for several exciting next steps. In Reactions Signs of Chemical Reactions, you will learn to recognize when a chemical reaction is happening. In Types of Changes Physical vs. Chemical Changes, you will use your knowledge of chemical properties to tell the two types of changes apart. You will also apply what you know in Mineral Properties Physical and Chemical Properties, Material Selection Properties and Applications, and Solution Properties Concentration and Solubility.