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Chapter 13: Problem 18

Classify the following two changes as physical or chemical. Explain your reasoning. \(\mathrm{a} . \mathrm{CaCO}_{3}(s)+\mathrm{H}_{2} \mathrm{SO}_{4}(a q) \longrightarrow \mathrm{CaSO}_{4}(a q)+\mathrm{CO}_{2}(g)+\mathrm{H}_{2} \mathrm{O}(l)\) b. \(\operatorname{NaCl}(s) \longrightarrow \mathrm{NaCl}(l)\)

Short Answer

Expert verified
Change (a) is chemical; change (b) is physical.

Step by step solution

01

Understanding Chemical and Physical Changes

A chemical change results in the formation of one or more new substances with different properties, while a physical change involves a change in state or form without forming new substances. Identifying these changes involves examining whether new substances are produced.
02

Analyzing Change (a): Reaction of CaCO3 with H2SO4

In the reaction \(\mathrm{CaCO}_{3}(s)+\mathrm{H}_{2} \mathrm{SO}_{4}(a q)\longrightarrow \mathrm{CaSO}_{4}(a q)+\mathrm{CO}_{2}(g)+\mathrm{H}_{2}\mathrm{O}(l)\), new substances are formed: calcium sulfate, carbon dioxide, and water. The original substances, calcium carbonate and sulfuric acid, are transformed into different substances, indicating a chemical change.
03

Evaluating Change (b): Phase Change of NaCl

In the process \(\operatorname{NaCl}(s) \longrightarrow \mathrm{NaCl}(l)\), sodium chloride changes from a solid to a liquid state due to an increase in temperature (melting). The chemical identity of NaCl remains the same, indicating a physical change.
04

Concluding Classification

From the analysis, Change (a) involves a chemical reaction with new products formed, classifying it as a chemical change. Change (b), involving a phase change without altering the chemical identity, is classified as a physical change.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Chemical Reactions
Chemical reactions are fascinating processes where substances, known as reactants, transform into new substances called products. During a chemical reaction, the molecular structure of the reactants changes. This change results in the formation of new substances with entirely different properties. Here are some key characteristics of chemical reactions:
  • The original substances are transformed into new substances.
  • There is usually a noticeable energy change, such as heat, light, or sound.
  • Reactants are consumed, and products are formed.
When you mix baking soda with vinegar, for example, you create an explosive chemical reaction that forms carbon dioxide gas, demonstrating how reactants change into products.
Phase Changes
Phase changes are transformations that occur between different states of matter: solid, liquid, and gas. While these changes may alter the form or appearance of a substance, they do not change its chemical identity. There are several types of phase changes:
  • Melting: when a solid becomes a liquid (e.g., ice melting to water).
  • Freezing: when a liquid becomes a solid (e.g., water freezing to ice).
  • Vaporization: when a liquid turns into a gas (e.g., water boiling to steam).
  • Condensation: when a gas becomes a liquid (e.g., steam condensing to water).
  • Sublimation: when a solid changes directly into a gas (e.g., dry ice becoming carbon dioxide gas).
These changes involve the absorption or release of energy, and though they might seem dramatic, the substance itself stays the same at the molecular level.
Substance Formation
Substance formation is a key result of chemical reactions. It is when one or more new substances are produced, often with new properties and characteristics. The formation of a new substance indicates that a chemical reaction has occurred. Let's look at some examples:
  • When hydrogen and oxygen gases combine, they form water, a completely different substance.
  • Burning wood in a fireplace produces ash, carbon dioxide, and water vapor, all new substances.
  • The rusting of iron results in iron oxide, a new compound.
In substance formation, the key is the rearrangement of atoms to create new molecular structures.
Calcium Carbonate Reaction
The reaction of calcium carbonate (\( \mathrm{CaCO}_{3} \)) with sulfuric acid (\( \mathrm{H}_{2} \mathrm{SO}_{4}\)) is a classic example of a chemical change. This reaction produces calcium sulfate (\( \mathrm{CaSO}_{4}\)), carbon dioxide (\( \mathrm{CO}_{2}\)), and water (\( \mathrm{H}_{2} \mathrm{O}\)).Here's what happens in this reaction:
  • Calcium carbonate, originally a solid, reacts with aqueous sulfuric acid.
  • New substances, like calcium sulfate, which can easily dissolve in water, are formed.
  • Gaseous carbon dioxide is released, often observed as bubbles.
  • The formation of water also helps in dissolving some of the products.
This reaction exemplifies how original substances can transform into completely new materials with different physical and chemical properties.
Sodium Chloride Melting
The melting of sodium chloride (\( \mathrm{NaCl} \)) is a process that demonstrates a phase change. When heated, the solid form of sodium chloride becomes a liquid. This change involves simply altering the state of the substance from solid to liquid without changing its chemical identity.Key insights into sodium chloride melting:
  • The solid crystal structure of \( \mathrm{NaCl} \) breaks down into a liquid form upon heating.
  • All salt particles remain sodium chloride; no new substances are formed.
  • The melting point of sodium chloride is very high, around 801掳C (1474掳F) due to strong ionic bonds.
By understanding the melting process, we see how energy applied as heat can induce significant changes in the state of matter while leaving the chemical composition intact.

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Most popular questions from this chapter

Look up chloramine, NH_ \(_{2} \mathrm{Cl}\) , and hydrazine, \(\mathrm{N}_{2} \mathrm{H}_{4},\) on the Internet. Describe the toxicity of each compound.

Explain why dissolving can be described as either a physical or chemical change.

Classify these reactions as combination, decomposition, single exchange, or double exchange. Copy the equations, fill in any missing products, and write a balanced equation for each reaction. a. \(\mathrm{NaOH}(a q)+\mathrm{HNO}_{3}(a q) \longrightarrow \operatorname{NaNO}_{3}(a q)+\) ________ \((l)\) b. \(C_{2} \mathrm{H}_{4}(g)+\mathrm{Cl}_{2}(g) \longrightarrow\) ________ \((g)\) c. \(\mathrm{Cl}_{2}(g)+\mathrm{MgBr}_{2}(s) \longrightarrow \mathrm{Br}_{2}(s)+\) ________ \((s)\)

Solid lithium reacts with aqueous hydrochloric acid to produce hydrogen gas and aqueous lithium chloride: \(\mathrm{Li}(s)+\mathrm{HCl}(a q) \longrightarrow \mathrm{H}_{2}(g)+\)___________________ Predict the missing product, balance the equation, and explain how these toxic substances could enter the body.

What would you have to do to prove that matter is conserved when a piece of paper is burned?
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