Question

Hydrogen gas and chlorine gas react to make hydrogen chloride gas with an accompanying enthalpy change of \(-184 \mathrm{~kJ}\). Is this process endothermic or exothermic?

Short answer

The process is exothermic because the enthalpy change is negative.

Step-by-step solution

Understand the Sign of Enthalpy Change

To determine whether a process is endothermic or exothermic, we need to look at the sign of the enthalpy change. An exothermic reaction releases energy, which means the enthalpy change is negative. An endothermic reaction absorbs energy, which means the enthalpy change is positive.

Analyze the Given Enthalpy Change

The problem states that the enthalpy change for the reaction is \(-184 \, \text{kJ}\). The negative sign indicates that energy is being released during the reaction.

Determine the Type of Reaction

Since the enthalpy change is negative \((-184 \, \text{kJ})\), it confirms that energy is released to the surroundings. Therefore, this reaction is exothermic.

Key concepts

enthalpy change

Enthalpy change refers to the amount of heat energy absorbed or released during a chemical reaction. It is represented by the symbol \(\Delta H\), and indicates whether a reaction takes in or gives out energy. The value of enthalpy change can either be positive or negative.

A positive enthalpy change (\(\Delta H > 0\)) signifies that the reaction absorbs energy from the surroundings, making it endothermic.

Conversely, a negative enthalpy change (\(\Delta H < 0\)) means that energy is released to the surroundings, indicating an exothermic reaction.

This concept is crucial for understanding how energy transformations occur during chemical processes. It helps chemists determine the energy balance of reactions and their potential impact.

energy release

Energy release in chemical reactions occurs when bonds are formed. During a reaction, atoms rearrange, breaking existing chemical bonds and forming new ones. This rearrangement either absorbs or releases energy depending on the nature of the bonds involved.

In exothermic reactions, the energy released in forming new bonds is greater than the energy needed to break existing bonds. This results in the release of energy to the surroundings, often in the form of heat or light. For instance, when we burn natural gas in a stove, energy is released, warming our pots and pans.

• Exothermic reactions often feel warm or hot since they release heat.
• Common examples include combustion, such as burning wood or gasoline.

Understanding energy release helps predict the direction and feasibility of chemical reactions, as well as their applicability in practical situations.

endothermic vs exothermic reactions

Endothermic and exothermic reactions describe two types of processes based on energy changes.

**Endothermic Reactions:**

• These reactions absorb energy from their surroundings.
• Characterized by a positive enthalpy change (\(\Delta H > 0\)).
• Commonly observed in photosynthesis, where plants absorb sunlight to convert carbon dioxide and water into glucose and oxygen.

**Exothermic Reactions:**

• These reactions release energy to their surroundings.
• Characterized by a negative enthalpy change (\(\Delta H < 0\)).
• Examples include combustion and many oxidation-reduction reactions, such as the rusting of iron.

Identifying whether a reaction is endothermic or exothermic allows scientists to harness these processes for various applications, from energy production to industrial manufacturing. Understanding the distinction can also help one predict the energetic behavior of new or unfamiliar chemical reactions.