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Chapter 6: Problem 42

Write the equation for calculating the enthalpy of a reaction. Define all the terms.

Short Answer

Expert verified
The equation is \( \Delta H = H_{products} - H_{reactants} \). \( \Delta H \) is the enthalpy change, \( H_{products} \) is the enthalpy of products, and \( H_{reactants} \) is the enthalpy of reactants.

Step by step solution

01

Understand What Enthalpy Is

Enthalpy is a measure of the total heat content in a thermodynamic system. It is a state function that is used to quantify the heat change during a chemical reaction at constant pressure.
02

Identify the Equation for Enthalpy Change

The enthalpy change of a reaction, denoted as \( \Delta H \), is given by the equation: \[ \Delta H = H_{products} - H_{reactants} \]Here, \( H_{products} \) is the enthalpy of the products and \( H_{reactants} \) is the enthalpy of the reactants.
03

Explanation of Terms

- \( \Delta H \) (Delta H) represents the change in enthalpy or heat of the reaction.- \( H_{products} \) is the total enthalpy of all the products of the reaction.- \( H_{reactants} \) is the total enthalpy of all the reactants before the reaction takes place.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Thermodynamics
Thermodynamics is the science of energy and its transformations. It studies how energy moves between a system and its surroundings. When we talk about chemical reactions, thermodynamics helps us analyze heat changes and energy flow.
One important goal is to understand how much energy is exchanged as heat. This is crucial for studying reactions at a constant pressure, which is common in labs and industry.
  • Energy exchanged can influence the conditions under which reactions occur.
  • It helps predict whether a reaction will release or absorb energy, influencing temperature changes.
Understanding thermodynamics allows chemists to control and optimize reactions for desired outcomes.
State Function
State functions are properties that only depend on the current state of a system, not the path taken to reach that state. Enthalpy, represented by the symbol H, is one such state function.
Because enthalpy is a state function:
  • It means the change in enthalpy (\( \Delta H \)) is independent of how reactants are converted into products.
  • It allows us to focus on the initial and final states without worrying about the intermediate steps.
    This is very useful in chemistry because it simplifies calculations and predictions.
Enthalpy is especially important because it measures the heat absorbed or released during reactions, helping analyze energy efficiency.
Chemical Reaction
A chemical reaction involves rearrangement of atoms to transform reactants into products. During this process, bonds break and new ones form.
Chemical reactions are classified as:
  • Endothermic: absorb heat from the surroundings, making them feel cold.
  • Exothermic: release heat during the reaction, making them feel warm.
Understanding whether a reaction is endothermic or exothermic is vital. It affects everything from reaction conditions to safety considerations. Analyzing the enthalpy change (\( \Delta H \)) helps in this classification.
This is why carefully monitoring enthalpy is necessary - it helps predict and control reactions effectively.
Enthalpy of Products and Reactants
The enthalpy of products and reactants is central in determining the enthalpy change of a reaction. Each substance involved has a specific enthalpy that contributes to the total heat content.
The equation:\[ \Delta H = H_{products} - H_{reactants} \]
  • \( H_{products} \) represents the total heat content of all products after the reaction.
  • \( H_{reactants} \) signifies the total heat content before the reaction starts.
The enthalpy change \( \Delta H \) indicates the net heat absorbed or released. It's crucial for understanding whether the overall process is endothermic or exothermic.
This understanding enables more controlled and efficient chemical reactions, helping to achieve desirable results.

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Most popular questions from this chapter

The work done to compress a gas is \(74 \mathrm{~J}\). As a result, \(26 \mathrm{~J}\) of heat is given off to the surroundings. Calculate the change in energy of the gas.

The internal energy of an ideal gas depends only on its temperature. Do a first-law analysis of this process. A sample of an ideal gas is allowed to expand at constant temperature against atmospheric pressure. (a) Does the gas do work on its surroundings? (b) Isthere heat exchange between the system and the surroundings? If so, in which direction? (c) What is \(\Delta U\) for the gas for this process?

What is meant by the standard-state condition?

Decomposition reactions are usually endothermic, whereas combination reactions are usually exothermic. Give a qualitative explanation for these trends.

Define these terms: enthalpy, enthalpy of reaction. Under what condition is the heat of a reaction equal to the enthalpy change of the same reaction?
See all solutions

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