Chemical Reaction: Chemical Change - Online Tutor, Practice Problems & Exam Prep

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 changes in color. For instance, we can have a solution that's light pink transitioning to violet or darker purple. We can observe the formation of gas, as visible through bubbles forming. We can also see precipitate formation; precipitate is simply a solid. Additionally, we can observe changes in temperature. These are changes that we can see with our own eyes, providing 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 illustrate 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. Now let's talk about the different chemical formulas as well as symbols involved in this chemical equation.

So these symbols of chemical equations, 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 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 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've 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're 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 (Δ). 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). This would represent our chemical equation. This chemical equation is already balanced, we don't have to worry about that just yet. This would be our balanced chemical equation that shows the decomposition of our solid sodium carbonate into sodium oxide and carbon dioxide gas.