Question

Endothermic reaction is one in which (a) heat is converted into electricity (b) heat is absorbed (c) heat is given out (d) heat is converted into mechanical work

Short answer

The correct answer is (b) heat is absorbed.

Step-by-step solution

Understand the Term

An endothermic process describes a reaction where energy (as heat) flows from the surroundings into the system. In an endothermic reaction, the system absorbs heat energy from its surroundings.

Match the Definition

From the given options, choose the one that matches the definition mentioned in Step 1.

Choose the Correct Answer

Matching the definition to the options, option (b) 'heat is absorbed' correctly describes an endothermic reaction.

Key concepts

Thermochemistry

Thermochemistry is the study of heat change in chemical reactions. Essentially, it looks at how energy in the form of heat is transferred during a chemical process, whether it's released into the environment, as in exothermic reactions, or absorbed from the surroundings, like in endothermic reactions. A key concept in thermochemistry is the law of conservation of energy, which states that energy cannot be created or destroyed, only transformed.

Understanding endothermic reactions is part of mastering thermochemistry. These are reactions that absorb heat, leading to a decrease in temperature of the environment because energy is being taken in. In a classroom experiment, you might feel a container turning cold when an endothermic reaction occurs inside it. This temperature change is an important clue that helps distinguish endothermic from other types of reactions.

Chemical Thermodynamics

Chemical thermodynamics goes a step beyond thermochemistry by looking at the broader relationship between physical changes, chemical reactions, and energy change. It deals with the effects of temperature, pressure, and volume on chemical systems and how these systems tend toward equilibrium, where the forward and reverse reaction rates are equal, at least within a closed system.

An endothermic reaction, when viewed through thermodynamics, involves not just a transfer of heat but a shift in internal energy (\( \triangle U \)). When the system absorbs heat, the internal energy increases. Chemical thermodynamics will quantify this energy change and predict whether a reaction is spontaneous based on entropy, enthalpy, temperature, and Gibb's energy equations. Understanding these concepts is fundamental to grasping energy flow in reactions.

Heat Absorption in Reactions

Heat absorption is a critical aspect of endothermic reactions. In these reactions, energy as heat flows from the surroundings into the system, causing the surroundings to feel cooler. For example, when ammonium nitrate is dissolved in water, it absorbs heat from the water, resulting in a cold pack commonly used for injuries.

To measure the amount of heat absorbed, scientists use a unit called joule or sometimes calorie. The specific heat capacity, which is the amount of heat required to raise the temperature of a substance by one degree Celsius, is an important factor in calculating heat absorption. In an endothermic reaction, the reaction will not proceed unless sufficient heat is supplied, highlighting the importance of this energy exchange.

Energy Flow in Chemical Processes

Energy flow in chemical processes looks at how energy is transferred and transformed in chemical reactions. In an endothermic reaction, this energy flow is from the surroundings to the system. In addition to heat, this energy can be in forms such as light or electricity, depending on the nature of the reaction.

Understanding the energy flow allows scientists and students to predict reaction behavior under various conditions. For example, if a reaction is endothermic, increasing the temperature typically increases the rate of reaction as more heat is available to be absorbed. In contrast, cooling the system would slow down the reaction. This knowledge is crucial when designing chemical processes in industrial applications, where control over reaction rates and energy efficiency are paramount.