Chemical Reaction: Chemical Change: Study with Video Lessons, Practice Problems & Examples

A chemical reaction signifies a chemical change where reactants undergo transformations, breaking and forming chemical bonds. Observable evidence includes color change, gas formation (bubbles), precipitate (solid), and temperature changes. Chemical equations represent these reactions using symbols and formulas, with the reaction arrow indicating the process. States of matter are denoted as solid (s), liquid (l), gas (g), and aqueous (aq) for compounds in solution. Understanding these concepts is crucial for grasping chemical processes and their implications in various scientific fields.

Chemical Reaction: Chemical Change Concept 1

Recall a chemical reaction as an example of a chemical change. A chemical reaction itself involves chemical bonds that are broken in reactants, and new chemical bonds that are formed in products. Now, we're going to say here that through the use of our senses, we can observe many of these chemical changes or chemical reactions taking place. So, some observable evidence of a chemical reaction includes a change in color. So, we can have a solution that's light pink transitioning to maybe violet or darker purple. We can have the formation of gas, so we can see bubbles forming. Or we can have precipitate. Precipitate is just a solid. We also could observe changes in temperature. These are changes that we can see with our own eyes that are evidence that a chemical reaction has taken place.

Chemical Reaction: Chemical Change Example 1

What happens on a molecular level when a chemical reaction occurs? A, bonds are broken, B, bonds are formed, C, temperature increases or decreases, or is it D, all of the above? Well, we talked about this earlier that there are certain changes that are observable through our senses that are evidence of a chemical reaction occurring. Now bonds being broken or formed, it's harder to see that sometimes, but these are evidence that a chemical reaction has happened even on a molecular level. And we also said that changes in temperature were an observable change that illustrates a chemical reaction has occurred. So A, B, and C are all evidence of a chemical reaction occurring. Therefore, the answer is D, all of the above.

Chemical Reaction: Chemical Change Concept 2

Now a chemical equation is just an expression that uses chemical formulas and symbols to represent chemical reactions. So here what we have is we have 2 and this is called sodium bicarbonate, breaking down to give us sodium carbonate, water, and carbon dioxide:

2 NaHCO 3 → Na 2 CO 3 + H O l + CO 2 g

Let's talk about the different chemical formulas as well as symbols involved in this chemical equation. Here we have our arrow. We call this our reaction arrow. It's a way of saying that our reaction proceeds, our reactants undergo a change to form products. Next, we have this little triangle here. This triangle is a way of talking about heat being involved. So instead of literally writing the word "heat," you can substitute in this triangle for it.

The next are the different states that exist in terms of our compound within a chemical reaction. So here, this "s" means that it is a solid. So in the chemical equation up above, sodium bicarbonate is a solid, and sodium carbonate is a solid. "l" means liquid, so water here is a liquid. "g" here means gas, so carbon dioxide here is a gas. And here, this one we don’t have any chemical equation but it does pop up in a lot of types of chemical equations. "aq" stands for aqueous. What that means is that our compound or molecule in question is dissolved in a solvent like water. So when you see aqueous for a compound, that means it is in a water solution. Okay. So you have taken the compound and placed it into water, and therefore, it's surrounded by water and therefore, it is in an aqueous state. So just keep in mind these different types of chemical formulas and symbols that are pretty customary with any type of chemical equation that you are going to eventually start seeing.

Chemical Reaction: Chemical Change Example 2

So here it says write a chemical equation using correct formulas and symbols for the decomposition of solid sodium carbonate at high temperature to produce solid sodium oxide and carbon dioxide gas. Alright. So they're telling me that I have solid sodium carbonate. Sodium carbonate, remember, is Na₂CO₃ (solid). They're saying that it's decomposing, I mean, it's breaking down. And they're saying high temperature, which means heat is involved. So you can put a triangle. Here it's saying that we're producing sodium oxide. Remember sodium is in group 1A, so it's +1 in its charge. Oxide is O^2-. Remember, when the numbers in the charges are different, they don't cancel out, they crisscross. So that would be Na₂O (solid), plus carbon dioxide which is CO₂ (gas). Here, this would represent our chemical equation. This chemical equation is already balanced; we don't have to worry about that just, quite yet. This would be our balanced chemical equation that shows the decomposition of our solid sodium carbonate into sodium oxide and carbon dioxide gas.

Here’s what students ask on this topic:

What are some observable signs of a chemical reaction?

Observable signs of a chemical reaction include a change in color, formation of gas (bubbles), formation of a precipitate (solid), and changes in temperature. For example, a solution might change from light pink to violet, indicating a chemical change. Bubbles forming in a liquid suggest gas production, while a solid forming in a solution indicates a precipitate. Temperature changes, either exothermic (releasing heat) or endothermic (absorbing heat), also signal a chemical reaction. These signs help us identify when a chemical reaction has occurred.

What is a chemical equation and what do its symbols represent?

A chemical equation is an expression using chemical formulas and symbols to represent a chemical reaction. The reaction arrow (→) indicates the direction of the reaction, showing reactants transforming into products. Symbols like (s), (l), (g), and (aq) denote the states of matter: solid, liquid, gas, and aqueous (dissolved in water), respectively. For example, in the equation NaHCO₃ (s) → Na₂CO₃ (s) + H₂O (l) + CO₂ (g), sodium bicarbonate (solid) breaks down into sodium carbonate (solid), water (liquid), and carbon dioxide (gas).

How do chemical bonds change during a chemical reaction?

During a chemical reaction, chemical bonds in the reactants are broken, and new bonds are formed in the products. This process involves the rearrangement of atoms to create new substances. For example, in the reaction 2H₂ (g) + O₂ (g) → 2H₂O (l), the bonds between hydrogen molecules (H₂) and oxygen molecules (O₂) are broken, and new bonds are formed to create water (H₂O). This bond-breaking and bond-forming process is fundamental to all chemical reactions.

What does the symbol (aq) mean in a chemical equation?

The symbol (aq) in a chemical equation stands for 'aqueous,' indicating that the compound is dissolved in water. For example, NaCl (aq) means sodium chloride is dissolved in water, forming an aqueous solution. This state is important in many chemical reactions, especially in biological and environmental processes, where substances often react in water-based solutions.

Why is it important to understand the states of matter in a chemical equation?

Understanding the states of matter in a chemical equation is crucial because it provides information about the physical form of the reactants and products, which can affect the reaction's behavior and outcome. For instance, reactions involving gases may require different conditions (e.g., pressure) compared to those involving solids or liquids. Knowing whether a substance is solid (s), liquid (l), gas (g), or aqueous (aq) helps predict reaction conditions, product formation, and the overall feasibility of the reaction.