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Chapter 1: Problem 21

When calcium chloride \(\left(\mathrm{CaCl}_{2}\right)\) dissolves in water, the temperature of the water increases dramatically. During this reaction, heat transfers from (A) the reactants to the products (B) the reactants to the system (C) the system to the surroundings (D) the products to the surroundings

Short Answer

Expert verified
The correct choice is (C) the system to the surroundings. This is because during the exothermic process of calcium chloride dissolving in water, energy (in the form of heat) is transferred from the system (calcium chloride + water) to the surroundings.

Step by step solution

01

Understand the Process

Recognize the process described - dissolving of calcium chloride in water. During this process, heat is released, which means it is an exothermic reaction.
02

Identify the System and the Surroundings

We have the system as the calcium chloride and water, while the surroundings consist everything outside of this system. In simpler terms, the surroundings are what the system interacts with to gain or lose energy.
03

Determine the Direction of Heat Transfer

Since the dissolving of calcium chloride in water releases heat, it means that this energy is transferred from the system to the surroundings.

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Key Concepts

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

Exothermic Reaction
Exothermic reactions are fascinating processes where energy is released, usually in the form of heat. When calcium chloride (\(\text{CaCl}_{2}\)) dissolves in water, it creates an exothermic reaction. The increase in temperature of the water indicates that heat is being released. This release of energy makes the reaction exothermic. Such reactions are common in everyday life, and they often create warmth or even light. Key features of exothermic reactions include:
  • Release of heat energy.
  • Increase in temperature of the surroundings.
  • Often feels warm to the touch.
Understanding these reactions helps us design things like hand warmers and instant heat packs, exploiting the natural release of heat.
Heat Transfer
Heat transfer is central to understanding how energy moves during reactions. When calcium chloride dissolves in water, the heat generated transfers to its surroundings. This movement of energy is known as heat transfer. It can happen in various ways:
  • Conduction: Direct transfer through contact.
  • Convection: Transfer through fluid movement.
  • Radiation: Transfer through electromagnetic waves.
For dissolving \(\text{CaCl}_{2}\), the heat primarily moves by conduction. The system releases heat, which then flows to the surrounding water and air. Understanding heat transfer helps in figuring out how and where energy goes during chemical processes.
System and Surroundings
In chemistry, distinguishing between the system and surroundings is crucial. The system typically includes the components involved in the reaction鈥攊n this case, the calcium chloride and water. Everything outside this particular setup is labeled as the surroundings. Think of the system as a small bubble where the reaction occurs, and the surroundings as everything else outside that bubble. This distinction helps:
  • Identify where changes and interactions occur.
  • Determine where energy flows.
  • Consider effects of reactions on the environment.
With \(\text{CaCl}_{2}\) dissolved in water, the heat from this system is transferred to surrounding areas, like the air or nearby objects.
Dissolution Process
The dissolution process involves a solute (like calcium chloride) mixing into a solvent (like water) to form a solution. For calcium chloride, dissolving is more than just mixing; it involves breaking down solid crystal structures. When \(\text{CaCl}_{2}\) dissolves, water molecules separate the ions in the compound, facilitating their movement around in the liquid. This process:
  • Breaks ionic bonds in the solute.
  • Hydrates the ions, stabilizing them in solution.
  • Is often associated with heat changes.
The exothermic nature of this process means it releases heat, raising the temperature of the resulting solution. Understanding dissolution is key in fields like pharmaceuticals, where dissolving substances at the right time and place is vital to drug effectiveness.

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Most popular questions from this chapter

Silver sulfate, \(\mathrm{Ag}_{2} \mathrm{SO}_{4}\) , has a solubility product constant of \(1.0 \times 10^{-5} .\) The below diagram shows the products of a precipitation reaction in which some silver sulfate was formed. (Diagram Can't Copy) Which ion concentrations below would have led the precipitate to form? (A) \(\left[\mathrm{Ag}^{+}\right]=0.01 M\left[\mathrm{SO}_{4}^{2-}\right]=0.01 M\) (B) \(\left[\mathrm{Ag}^{+}\right]=0.10 M\left[\mathrm{SO}_{4}^{2-}\right]=0.01 M\) (C) \(\left[\mathrm{Ag}^{+}\right]=0.01 M\left[\mathrm{SO}_{4}^{2-}\right]=0.10 M\) (D) This is impossible to determine without knowing the total volume of the solution.

\(\mathrm{H}_{2}(g)+\mathrm{F}_{2}(g) \rightarrow 2 \mathrm{HF}(g)\) Gaseous hydrogen and fluorine combine in the reaction above to form hydrogen fluride with an enthalpy change of \(-540 \mathrm{kJ}\) . What is the value of the heat of formation of \(\mathrm{HF}(g) ?\) (A) \(-1,080 \mathrm{kJ} / \mathrm{mol}\) (B) \(-270 \mathrm{kJ} / \mathrm{mol}\) (C) 270 \(\mathrm{kJ} / \mathrm{mol}\) (D) 540 \(\mathrm{kJ} / \mathrm{mol}\)

Questions 45-48 refer to the following. Inside a calorimeter, 100.0 \(\mathrm{mL}\) of 1.0 \(\mathrm{M}\) hydrocyanic acid (HCN), a weak acid, and 100.0 \(\mathrm{mL}\) of 0.50 \(\mathrm{M}\) sodium hydroxide are mixed. The temperature of the mixture rises from \(21.5^{\circ} \mathrm{C}\) to \(28.5^{\circ} \mathrm{C}\) . The specific heat of the mixture is approximately \(4.2 \mathrm{J} / \mathrm{g}^{\circ} \mathrm{C},\) and the density is identical to that of water. What is the approximate amount of heat released during the reaction? \(\begin{array}{ll}{\text { (A) }} & {1.5 \mathrm{kJ}} \\ {\text { (B) }} & {2.9 \mathrm{kJ}} \\ {\text { (C) }} & {5.9 \mathrm{kJ}} \\ {\text { (D) }} & {11.8 \mathrm{kJ}}\end{array}\)

\(\begin{array}{ll}{\mathrm{C}(s)+2 \mathrm{H}_{2}(g) \rightarrow \mathrm{CH}_{4}(g)} & {\Delta H^{\circ}=x} \\\ {\mathrm{C}(s)+\mathrm{O}_{2}(g) \rightarrow \mathrm{CO}_{2}(g)} & {\Delta H^{\circ}=y} \\ {\mathrm{H}_{2}(g)+\frac{1}{2} \mathrm{O}_{2}(g) \rightarrow \mathrm{H}_{2} \mathrm{O}(l)} & {\Delta H^{\circ}=\mathrm{z}}\end{array}\) Based on the information given above, what is \(\Delta H^{\circ}\) for the following reaction? \(\mathrm{CH}_{4}(g)+2 \mathrm{O}_{2}(g) \rightarrow \mathrm{CO}_{2}(g)+2 \mathrm{H}_{2} \mathrm{O}(l)\) (A) \(x+y+z\) (B) \(x+y-z\) (C) \(z+y-2 x\) (D) \(2 z+y-x\)

Even though it is a noble gas, xenon is known to form bonds with other elements. Which element from the options below would xenon most likely be able to bond with? (A) Lithium (B) Argon (C) Fluorine (D) Carbon
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