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Chapter 18: Problem 118

What is the difference between an exothermic and an endothermic reaction? (Chapter 15)

Short Answer

Expert verified
Exothermic reactions release energy, increasing surrounding temperature, while endothermic reactions absorb energy, decreasing surrounding temperature.

Step by step solution

01

Understand Exothermic Reactions

Exothermic reactions are chemical reactions that release energy to the surroundings, usually in the form of heat. This results in an increase in the temperature of the surroundings. A classic example is combustion, such as burning wood or gasoline.
02

Understand Endothermic Reactions

Endothermic reactions are chemical reactions that absorb energy from the surroundings. They result in a decrease in the temperature of the surroundings. Examples include photosynthesis in plants and the reaction of barium hydroxide with ammonium thiocyanate.
03

Identify Key Differences

The key difference between exothermic and endothermic reactions is their energy flow. Exothermic reactions release energy, typically increasing the temperature of their surroundings, while endothermic reactions absorb energy, leading to a temperature decrease in their surroundings.

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Key Concepts

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

Energy Release
Energy release is a fundamental concept when discussing exothermic and endothermic reactions. In every chemical reaction, bonds between atoms in reactants are broken, and new bonds in products are formed. This process is accompanied by the transfer of energy.

  • **Exothermic Reactions**: In these reactions, more energy is released when new bonds are formed in the products than is required to break the bonds in the reactants. This excess energy is released into the surroundings, often as heat. For example, during the combustion of wood or gasoline, chemical energy is transformed into thermal energy, which we can feel as heat.
  • **Endothermic Reactions**: Conversely, these reactions require more energy to break bonds in the reactants than is released when new bonds form. As a result, they absorb energy from their surroundings. A practical example of an endothermic reaction is photosynthesis, where plants absorb energy from sunlight to convert carbon dioxide and water into glucose and oxygen.
Understanding the energy release or absorption helps in predicting the temperature changes that accompany chemical reactions.
Temperature Change
Temperature change is a clear indicator of the type of chemical reaction taking place. During an exothermic reaction, the energy released increases the temperature of the surroundings.

  • **Exothermic Reactions**: Since these reactions give off energy, often as heat, you will notice an increase in temperature. Imagine touching a metal surface after an iron rusts in oxygen; the released heat from the reaction will have warmed up the metal surface.
  • **Endothermic Reactions**: These reactions absorb heat, resulting in a temperature decrease of the reaction's surrounding environment. For example, when barium hydroxide is mixed with ammonium thiocyanate, the solution becomes colder due to the absorption of thermal energy.
The change in temperature allows us to grasp and quantify the energy flows in chemical reactions.
Chemical Reactions
Chemical reactions involve the transformation of one or more substances into new substances. During this process, atoms are reorganized as old bonds break and new ones form. Exothermic and endothermic reactions are two fundamental types of chemical reactions, each with unique characteristics.

  • **Exothermic Reactions**: These are characterized by the release of energy, resulting in increased temperature of the environment. Example reactions include burning fuels and the reaction between NaOH and water. This signifies that the products are at a lower energy state than the reactants.
  • **Endothermic Reactions**: In contrast, these reactions absorb energy, leading to a cooling effect on the surroundings. Photosynthesis is one of the natural examples where energy from sunlight facilitates the creation of sugar from water and carbon dioxide.
Recognizing these reactions is crucial for understanding energy dynamics in chemical processes and practical applications, such as in energy solutions for heating or cooling.

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Most popular questions from this chapter

Design an Experiment Describe how you would design and perform a titration in which you use 0.250\(M \mathrm{HNO}_{3}\) to determine the molarity of a cesium hydroxide solution. Include the formula and net ionic equations.

Interpret Scientific Illustrations Sketch the shape of the approximate pH v. volume curve that would result from titrating a diprotic acid with a 0.10M NaOH solution.

Which of the following are polyprotic acids? Write successive ionization equations for the polyprotic acids in water. \begin{equation} \begin{array}{ll}{\text { a. } \mathrm{H}_{3} \mathrm{BO}_{3}} & {\text { c. HNO }_{3}} \\ {\text { b. } \mathrm{CH}_{3} \mathrm{COOH}} & {\text { d. } \mathrm{H}_{2} \mathrm{SeO}_{3}}\end{array} \end{equation}

Challenge Write an equation for a base equilibrium in which the base in the forward reaction is \(\mathrm{PO}_{4}^{3-}\) and the base in the reverse reaction is \(\mathrm{OH}^{-} .\)

Ammonia Cleaner Write the chemical equation and \(K_{\mathrm{b}}\) expression for the ionization of ammonia in water. How is it safe for a window cleaner to use a solution of ammonia, which is basic?
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