Problem 40 - Chemistry: An Atoms-Focused Approach

Question

In a simple "kitchen chemistry" experiment, some vinegar is poured into an empty soda bottle. A deflated balloon containing baking soda is stretched over the mouth of the bottle. Holding up the balloon and shaking it allows the baking soda to fall into the vinegar, which starts the following reaction and inflates the balloon: $$\begin{aligned} \mathrm{NaHCO}_{3}(a q)+\mathrm{CH}_{3} \mathrm{COOH}(a q) \rightarrow & \\ & \mathrm{CH}_{3} \mathrm{COONa}(a q)+\mathrm{CO}_{2}(g)+\mathrm{H}_{2} \mathrm{O}(\ell) \end{aligned}$$ If the contents of the bottle are the system, is work being done on the surroundings or on the system?

Step-by-Step Solution

Answer

Answer: Work is being done on the surroundings.

Step 1: Understand the concept of work in thermodynamics

In thermodynamics, work is the energy transferred to or from a system as a result of a force acting on the system. In this case, the system is the contents of the bottle (including the balloon) that are undergoing the chemical reaction, and the surroundings include everything outside the system.

Step 2: Analyze the chemical reaction

Given the reaction: $$\mathrm{NaHCO}_{3}(aq)+\mathrm{CH}_{3} \mathrm{COOH}(aq) \rightarrow \mathrm{CH}_{3} \mathrm{COONa}(aq)+\mathrm{CO}_{2}(g)+\mathrm{H}_{2} \mathrm{O}(\ell)$$ Baking soda (\(\mathrm{NaHCO}_{3}\)) reacts with vinegar (\(\mathrm{CH}_{3} \mathrm{COOH}\)) to produce sodium acetate (\(\mathrm{CH}_{3} \mathrm{COONa}\)), carbon dioxide gas (\(\mathrm{CO}_{2}\)), and water (\(\mathrm{H}_{2} \mathrm{O}\)). The carbon dioxide gas is responsible for inflating the balloon.

Step 3: Determine if work is done on the system or surroundings

As the carbon dioxide gas is produced, it increases the pressure inside the balloon. This pressure causes the balloon to expand, which in turn pushes against the surrounding air. As the balloon pushes against the outside air, it does work on the surroundings. Therefore, work is being done on the surroundings. So, the answer is: Work is being done on the surroundings.

Key Concepts

Chemical Reaction in the Experiment

In this simple kitchen experiment, we explore a chemical reaction between baking soda and vinegar. This reaction can be written as: \( \mathrm{NaHCO}_{3}(aq) + \mathrm{CH}_{3} \mathrm{COOH}(aq) \rightarrow \mathrm{CH}_{3} \mathrm{COONa}(aq) + \mathrm{CO}_{2}(g) + \mathrm{H}_{2} \mathrm{O}(\ell) \). Baking soda, scientifically known as sodium bicarbonate \((\mathrm{NaHCO}_{3})\), reacts with acetic acid \((\mathrm{CH}_{3} \mathrm{COOH})\) found in vinegar. This reaction leads to the formation of sodium acetate \((\mathrm{CH}_{3} \mathrm{COONa})\), water, and carbon dioxide gas \((\mathrm{CO}_{2})\). The reaction is a classic example illustrating how household ingredients can create a visible transformation. It's a marvel of chemistry where solid and liquid reactants produce gas and aqueous products.
Understanding such reactions showcases how molecules interact to form new substances, often with surprising real-world effects. Here, the focus is on the carbon dioxide production, a process that directly influences the physical changes in the experiment.

Gas Production and Its Effects

One of the most noticeable phenomena in this chemical reaction is the production of carbon dioxide gas \((\mathrm{CO}_{2})\). As the reaction progresses, the gas accumulates, having significant impacts on the immediate environment of the reaction—that is, inside the bottle and the balloon.
The amount of gas being generated increases quickly, causing it to exert pressure on the balloon walls. This pressure is what eventually inflates the balloon, a classic sign demonstrating the presence of gas.

• Carbon dioxide is a product of the reaction, ensuring there's ample expansion.
• The presence of gas is evidence of chemical change, indicating the reaction has occurred.

Understanding gas production is crucial in chemistry because it impacts several factors like temperature, volume, and pressure in a system, further guiding the study of chemical processes in reaction kinetics and gas laws.

Understanding Pressure Change

Pressure change is an important concept to comprehend in this experiment. As the carbon dioxide gas is generated, it leads to changes in pressure within our system, consisting of the vinegar, baking soda, and balloon. The increasing volume of CO2 gas forces the balloon to expand, essentially increasing the internal pressure.
When gas particles collide more often with the walls of the container (in this case, the balloon), they push outward, magnifying the internal pressure. This demonstrates the principle that gases expand to fill their container, and increased gas formation leads to increased pressure.

• The pressure change is entirely due to the creation of CO2 gas.
• Pressure changes like these cause observable changes such as the inflation of a balloon.

Pressure dynamics are key in thermodynamics and chemistry and affect how we understand gas behaviors under various conditions.

Work in Thermodynamics

In thermodynamics, work is defined as a force acting over a distance. When the chemical reaction occurs, and the carbon dioxide gas is produced, it causes the balloon to stretch and expand.
Here, work is done by the system on the surroundings. As the balloon inflates, it must push against the air around it. This force exerted by the balloon as it expands is an example of work being done.

• Work is a transfer of energy, often evident when a physical change takes place.
• In this scenario, the system (bottle contents) does work on its surroundings by expanding the balloon.
• Recognizing work in thermodynamics helps us understand energy transfer in processes.

Defining work within the context of thermodynamics aids in predicting and managing energy changes in both physical and chemical processes.