Problem 35 - Chemistry: An Atoms-Focused Approach

Question

Adding Drano to a clogged sink causes the drainpipe to get warm. What is the sign of \(\Delta H\) when Drano dissolves in water?

Step-by-Step Solution

Answer

Answer: The sign of the enthalpy change when Drano dissolves in water is negative, as heat is released during the process.

Step 1: Understand the given information

When Drano is added to water, it dissolves in water and causes the drainpipe to get warm.

Step 2: Examine the nature of the process

As the drainpipe gets warm, it means that heat is being released during the process of Drano dissolving in water.

Step 3: Determine the sign of \(\Delta H\)

Since heat is released during the process, the enthalpy change for the reaction is negative. Therefore, the sign of \(\Delta H\) when Drano dissolves in water is negative.

Key Concepts

Exothermic Reactions

When you drop Drano into a clogged sink and it begins to warm up, you might wonder what's happening. This warming is a sign of an exothermic reaction. Exothermic reactions are processes where heat is released into the surroundings. In simple terms, they give off heat.
In such reactions, the energy stored in the reactants is higher than that in the products. As a result, excess energy escapes as heat.
This process is quite common and happens in various everyday activities:

• Lighting a match
• Burning wood
• Combining certain chemicals like Drano with water

When Drano dissolves, the heat released implies energy exit, making it an exothermic process. That's why you feel the pipe getting warm. This energy release results in a negative enthalpy change, denoted as a negative \( \Delta H \).

Dissolution Process

The dissolution process is intriguing because it involves dissolving something into a liquid—like sugar in your tea. When Drano is dissolved in water, it triggers a dissolution process that releases heat.
You might ask, "Why does it release heat?" Here's why:Every dissolution involves breaking and forming bonds. For Drano, it requires energy to break the ionic bonds in the solid. However, when these ions interact with water molecules, new bonds form, releasing energy. If more energy is released than consumed in this process, the overall reaction is exothermic.
This difference in energy—where more is released than absorbed—causes the warming effect and shows a negative change in enthalpy (negative \( \Delta H \)), indicating the reaction is exothermic.

Thermochemistry

Thermochemistry might sound complex, but it's all about understanding energy changes during chemical reactions. It's a branch of chemistry that deals with the heat energy absorbed or released.
In our Drano example, thermochemistry helps explain why the pipe heats up.
Here's a breakdown:

• Thermochemistry uses the concept of enthalpy (H), which measures the total heat content of a system.
• In exothermic reactions like Drano's dissolution, the enthalpy change (\( \Delta H \) is negative, showing that heat is released.
• This helps predict how temperature changes during reactions.

Thermochemistry is vital for understanding diverse reactions, whether it's a household cleaning product or an industrial process. Mastering these basics is essential for predicting the energy changes in reactions.