What is the difference between a physical property and a chemical property?

A chemical reaction is like a dance where molecules exchange partners to create new substances. When you mix baking soda and vinegar, the fizz and bubbles you see are evidence of a chemical reaction. In this process, the substances involved, called reactants, are transformed into different products. This transformation happens through the breaking and forming of chemical bonds.

A reaction can release energy in the form of heat and light or absorb it, making it feel cold. The rate at which these reactions occur, the conditions needed, and the end result all depend on the specific characteristics of the reactants. In the classroom, you'll often observe reactions that result in gas production, color changes, or temperature shifts—all thrilling clues that a chemical reaction is taking place.

Understanding chemical reactions helps scientists create new materials, like medicines and sustainable fuels, and also explains how your body turns food into energy!

Matter can be likened to actors that can play different roles on the stage of the universe. Just as actors take on various characters, matter can exist in different states—solid, liquid, and gas—each with its own unique set of characteristics. Solids have a fixed shape and volume, like the ice in your freezer. Liquids, such as water, flow and fill the shape of their container but keep a constant volume. Gases, like the air you're breathing, expand to fill any space available.

Changing between these states is called a phase change and involves adding or removing energy. For instance, when you boil water, the liquid water absorbs heat, turning into steam—a gas. These transformations are physical changes because they don't affect the substance's core identity; water remains water whether it's ice, liquid, or steam.

Imagine if some people at a party mingled easily while others stayed put; reactivity in chemistry is somewhat similar. It's a measure of how readily a substance will undergo a chemical change. Some elements, like sodium, are social butterflies and react vigorously, even explosively, when introduced to water. Others, like gold, are the loners, content to remain in their elemental form without reacting much.

The conditions of the reaction—temperature, pressure, the presence of catalysts—can also alter how substances behave. Reactivity is fundamental in the creation of new materials and is a key consideration for everything from cooking food to powering batteries.

The enthalpy of formation is a bit like the cost of building a house—the total energy required to assemble the building blocks into a complete structure. In chemistry, it's the total energy change when one mole of a compound forms from its elements in their most stable states. Substances with low enthalpy of formation are like cost-effective homes to build, whereas those with high enthalpy cost more energy-wise.

This concept is crucial when discussing how much energy is stored within a substance and how that energy can be released or absorbed during reactions. For example, when gasoline burns in your car's engine, it releases a large amount of energy because the reactants have higher enthalpy than the products—a process that powers the vehicle. Understanding this concept helps us predict reaction outcomes and design energy-efficient processes in science and industry.