Question

For any given chemical reaction, if the sum of the enthalpies of atom combination for all of the reactants is more negative than the sum of the enthalpies of atom combination for all of the products, will the value of \(\Delta H[\) for the reaction be positive or negative? Explain your reasoning.

Short answer

\(\Delta H\) will be positive if the sum of the enthalpies of atom combination for all of the reactants is more negative than the sum of the enthalpies of atom combination for all of the products.

Step-by-step solution

Understanding the Concept of Enthalpy Change

Firstly, it's important to understand what \(\Delta H\) stands for. It refers to the change in enthalpy for a chemical reaction. The change is calculated by subtracting the total enthalpy of the reactants from the total enthalpy of the products.

Establishing the Relationship

Knowing this, if the enthalpy of atom combination for the reactants is more negative than that for the products, it means the reactants have a lower enthalpy than the products. Therefore, subtracting a smaller number (the enthalpy of the reactants) from a larger number (the enthalpy of the products) will result in a positive number.

Final conclusion

Thus, if the sum of the enthalpies of atom combination for all of the reactants is more negative than the sum of the enthalpies of atom combination for all of the products, the value of \(\Delta H\) for the reaction will be positive.

Key concepts

Chemical Thermodynamics

Chemical thermodynamics is a subdivision of thermodynamics that focuses on the energy changes involved in chemical reactions and phase changes. The central concept here is the enthalpy change (abla H), which represents the heat absorbed or released under constant pressure during a reaction.

Enthalpy itself is a state function, meaning that its value depends only on the current state of the system, not on how it got there. In the context of a chemical reaction, enthalpy changes provide insight into the energy flow and can determine whether a reaction is feasible under given conditions.

Understanding the enthalpy changes allows scientists and engineers to design processes that optimize energy use, whether it's in industrial manufacturing or biological systems. For students grappling with homework, a firm grasp of these principles allows for a better understanding of why reactions occur as they do.

Enthalpy of Atom Combination

The enthalpy of atom combination pertains to the energy change when atoms form chemical bonds to produce molecules. It is a specific instance of enthalpy change that reveals how much energy is required to break existing bonds or how much is released upon forming new bonds.

This concept can be somewhat abstract, so let's simplify it. Imagine you have a group of people holding hands, where each hand-hold represents a chemical bond. Breaking those hand-holds requires energy, similar to breaking bonds between atoms. Conversely, when people join hands to form new bonds, it can create a sense of satisfaction or release tension, akin to the release of energy when new bonds form in a molecule.

By comparing the enthalpy of atom combination for reactants and products in a reaction, we can determine whether energy will be absorbed or released overall during the reaction. This gives an immediate clue towards the reaction's abla H, whether it's endothermic (absorbs energy) or exothermic (releases energy).

Endothermic and Exothermic Reactions

Endothermic and exothermic reactions are two fundamental categories of reactions based on the direction of heat flow. In endothermic reactions, the system absorbs heat from the surroundings, resulting in a positive abla H. Think of it as a process needing a warm hug from the environment to proceed. Common examples include photosynthesis in plants and the baking soda-vinegar reaction used in science fair volcanoes.

In contrast, exothermic reactions release heat to the surroundings, showcasing a negative abla H. They're like a person who's too warm and takes off a coat, releasing heat. Combustion, rusting of iron, and chemical hand warmers operate on this principle.

The exercise improvement advice suggests using tangible examples, so consider this: when you activate a hand warmer, the chemicals inside undergo an exothermic reaction, releasing heat to warm your hands. This heat release corresponds to a negative abla H. On the other hand, when you use an ice pack that absorbs heat to become cold, it's facilitating an endothermic reaction, associated with a positive abla H. Understanding these concepts will allow students to better predict the outcomes of reactions they encounter in their studies and everyday life.