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Question Video: Identifying the Chemical Equation- with State Symbols- That Corresponds to a Chemical Statement Chemistry • 7th Grade

Solid calcium carbonate decomposes upon heating to produce carbon dioxide and solid calcium oxide. Which of the following symbolic equations with state symbols describes this chemical reaction? [A] CaCO₃ (g) ⟶ CaO (g) + CO₂ (s) [B] CaCO₃ (s) ⟶ CaO (s) + CO₂ (g) [C] Ca₂CO₃ (s) ⟶ CaO (g) + CO (g) [D] CaCO₃ (s) + O₂ (g) ⟶ CaO (s) + CO₂ (g) [E] CaCO₃ (s) + CO₂ (g) ⟶ CaO (s)

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Video Transcript

Solid calcium carbonate decomposes upon heating to produce carbon dioxide and solid calcium oxide. Which of the following symbolic equations with state symbols describes this chemical reaction? (A) CaCO3 gas reacts to form CaO gas plus CO2 solid. (B) CaCO3 solid reacts to form CaO solid plus CO2 gas. (C) Ca2CO3 solid reacts to form CaO gas plus CO gas. (D) CaCO3 solid plus O2 gas react to form CaO solid plus CO2 gas. (E) CaCO3 solid plus CO2 gas react to form CaO solid.

The first sentence in this question is a chemical statement. A chemical statement describes a chemical reaction in words. On the other hand, the answer choices are symbolic equations. Symbolic equations, also known as chemical equations, use chemical symbols to represent a reaction. For example, we see CaCO3 in several of the answer choices. Ca is the chemical symbol that represents the element calcium. C is the chemical symbol that represents carbon. And O is the chemical symbol that represents oxygen. Three is a subscript, which tells us how many of a particular type of atom is present. Altogether, CaCO3 is a chemical formula.

Chemical formulas in symbolic equations may also be followed by state symbols. The letter s, l, or g is written inside parentheses to tell if the species in the reaction is a solid liquid or gas. Our job in answering this question is to take the provided chemical statement and translate it into a correct symbolic equation. In the provided chemical statement, we can identify the word “decomposes” as a keyword. Chemical species that appear to the left of the keyword are the reactants of the chemical reaction. Only one species, calcium carbonate, appears to the left of the keyword. This means that the chemical reaction only has one reactant.

In examining answer choices (D) and (E), we see a plus sign is used on the left side of each equation. This tells us that there are two reactants. The correct symbolic equation can only contain one reactant. So we can eliminate these two answer choices because they contain too many reactants.

Let’s continue to read through the chemical statement. “Produce” is another keyword indicating that the reactant is forming products. To the right of this keyword, we can find the words that represent the products. Carbon dioxide and solid calcium oxide are separated by the word “and,” which means that there are two different products produced in the reaction.

Let’s create a basic word equation using the names of the reactants and products. To the left of the reaction arrow, let’s write calcium carbonate. And to the right of the reaction arrow, let’s write carbon dioxide plus calcium oxide. The chemical statement tells us the states of two of the species involved in the reaction. Both calcium carbonate and calcium oxide are solids. And even though it is not included in the chemical statement, we would expect carbon dioxide to be a gas.

Let’s rewrite our basic word equation using the correct state symbols. After calcium carbonate and calcium oxide, we’ll write an “s” inside parentheses. And after carbon dioxide, we’ll write a “g” inside parentheses.

Finally, we should be able to recognize that the chemical formula for carbon dioxide is CO2. Let’s go ahead and replace the words “carbon dioxide” with CO2 in our equation. We are able to eliminate choice (A) because the state symbol next to calcium carbonate and calcium oxide should be an “s” for solid. Also, the state symbol next to CO2 should be “g” for gas. Choice (A) is not a correct answer choice because the symbolic equation contains incorrect state symbols.

We can also eliminate answer choice (C) because the state symbol next to calcium oxide should be “s” for solid, not “g” for gas. In addition to this incorrect state symbol, the chemical formula for carbon dioxide is incorrect. In this equation, it is written as CO, which is the chemical formula for carbon monoxide.

This leaves only answer choice (B), which is our correct answer choice. Answer choice (B) is the correct symbolic equation with state symbols that matches the chemical statement provided in the question.

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