Question

According to Figure \(2,\) when 5 g of NH_{4} N O _ { 3 } \text { was } added to 100 g of \(\mathrm{H}_{2} \mathrm{O}\) , the temperature of the solution: F. decreased, because \(\Delta T\) was positive. G. decreased, because \(\Delta T\) was negative. H. increased, because \(\Delta T\) was positive. J. increased, because \(\Delta T\) was negative.

Short answer

Answer: The temperature of the solution decreases because ΔT is negative, indicating an endothermic process where heat is absorbed from the water.

Step-by-step solution

Understand ΔT and its relation to temperature

ΔT represents the change in temperature, which can be either positive or negative. If ΔT is positive, it means the final temperature is higher than the initial temperature, and the temperature has increased. If ΔT is negative, it means the final temperature is lower than the initial temperature, and the temperature has decreased.

Determine the effect of NH4NO3 on water temperature

When NH4NO3 is added to water, it is an endothermic process, meaning it absorbs heat from the surroundings. In this case, the heat is absorbed from the water, resulting in a decrease in the water's temperature.

Identify the correct answer choice

Since the temperature has decreased, this means that ΔT is negative. Based on the given answer choices, the correct answer is: G. decreased, because ΔT was negative.

Key concepts

Temperature Change

When we talk about temperature change in the context of chemistry, we're describing how the temperature of a substance increases or decreases in reaction to a process like a chemical reaction. Temperature is an indicator of the thermal energy within a system: when energy is added, the temperature rises, and when energy is removed, it drops.

In our exercise, the symbol (ΔT) represents the change in temperature. If (ΔT) is positive, it implies the temperature has increased, indicating an exothermic process where energy is released to the surroundings. Conversely, if (ΔT) is negative, the temperature has decreased, pointing to an endothermic process where energy is absorbed from the surroundings, thus cooling the system. Understanding this concept is paramount for interpreting and predicting the outcomes of chemical processes.

Chemical Reactions in Solutions

A chemical reaction in a solution occurs when substances dissolve and react in a solvent. The nature of this process—whether it releases or absorbs heat—gives us valuable information about the reaction.

For instance, when the ionic compound ammonium nitrate (NH_{4}NO_{3}) dissolves in water, it undergoes an endothermic reaction. The compound absorbs heat from the water to break the ionic bonds and become dispersed in the solution. This results in the water feeling cooler to the touch as the thermal energy (heat) is transferred from the water to the ammonium nitrate crystals. Recognizing how different substances behave in solution can help students predict the effects of dissolution and understand solution chemistry at a deeper level.

In educational content, we can enhance students' grasp by including visual aids such as plots or graphs showing temperature changes during dissolution. This tangible approach often makes the concept more accessible.

Enthalpy Change

The term enthalpy change, symbolized by (ΔH), represents the heat absorbed or released during a chemical reaction at constant pressure. It's a measurement of the energy change in a system. If (ΔH) is positive, it indicates an endothermic reaction, one that absorbs energy from the surroundings. Conversely, a negative (ΔH) suggests an exothermic reaction, which releases energy.

When ammonium nitrate is dissolved in water, the overall enthalpy change is positive because the dissolving process requires more energy to break the bonds than is released when new bonds form. This results in a net absorption of heat from the water, making the solution colder.

By associating enthalpy changes with temperature changes in chemical reactions in solutions, students can better understand the thermal dynamics of reactions. Learning to calculate enthalpy changes and relating them to laboratory or real-world scenarios underscores the practical application of thermodynamics in chemistry.