Question

Are the following processes exothermic or endothermic? a. When solid \(\mathrm{KBr}\) is dissolved in water, the solution gets coldel b. Natural gas \(\left(\mathrm{CH}_{4}\right)\) is burned in a furnace. c. When concentrated \(\mathrm{H}_{2} \mathrm{SO}_{4}\) is added to water, the solution get very hot. d. Water is boiled in a teakettle.

Short answer

a. Endothermic b. Exothermic c. Exothermic d. Endothermic

Step-by-step solution

Process a: Dissolving solid KBr in water

When solid KBr is dissolved in water, the process makes the solution colder. Since the solution cools down, it indicates that the process absorbs heat from the surroundings. Therefore, the process is endothermic.

Process b: Burning natural gas (CH4) in a furnace

When natural gas (CH4) is burned in a furnace, it releases a large amount of heat. This heat is what makes the furnace hot and able to heat up a home or other space. Since the process releases heat, it is an exothermic process.

Process c: Adding concentrated H2SO4 to water

When concentrated H2SO4 is added to water, the solution gets very hot. This is because the process releases heat, which increases the temperature of the solution. Since heat is released, this process is exothermic.

Process d: Boiling water in a teakettle

When water is boiled in a teakettle, heat is absorbed from the heat source to increase the water's temperature. Once the water reaches its boiling point, it continues to absorb heat in order to undergo the phase change from a liquid to a gas (steam). Since heat is being absorbed, the process of boiling water is endothermic. In summary: a. Dissolving solid KBr in water - Endothermic b. Burning natural gas (CH4) in a furnace - Exothermic c. Adding concentrated H2SO4 to water - Exothermic d. Boiling water in a teakettle - Endothermic

Key concepts

Endothermic Processes

Endothermic processes absorb heat from their surroundings, often resulting in a temperature drop. This absorption of energy occurs because the system requires heat to proceed or change, such as in chemical reactions or physical phase changes.
A classic example is dissolving potassium bromide ( KBr) in water. As seen in the original exercise, when KBr is dissolved, the surrounding solution gets colder.
This happens because the energy from the surroundings is transferred to break the bonds in the KBr lattice and facilitate its interaction with water molecules.

• Heat absorption
• Temperature decrease
• Energy requirement to break bonds

Exothermic Processes

Exothermic processes are the opposite of endothermic processes as they release heat to the surroundings, usually causing a temperature increase. This heat release is due to the energy being released when new bonds are formed during chemical reactions.
In the exercise, burning natural gas ( CH_4) in a furnace releases a large amount of heat, which shows the hallmark of an exothermic reaction.
Similarly, when concentrated H_2SO_4 is added to water, the solution becomes very hot due to the heat released from the chemical interaction.

• Heat release
• Temperature increase
• Energy release from bond formation

Heat Transfer in Chemical Reactions

Heat transfer is a vital concept in understanding chemical reactions, where either endothermic or exothermic processes can occur. In endothermic reactions, heat is absorbed to drive the reaction forward, often requiring an external energy source to maintain the reaction.
Conversely, in exothermic reactions, the reaction itself generates heat which can sustain or even accelerate the reaction.
Recognizing whether a process is endothermic or exothermic is crucial for controlling reactions in practical applications like industrial or laboratory settings.

• Endothermic: heat absorbed, often requiring external energy
• Exothermic: heat released, can sustain reaction

Phase Changes

Phase changes involve transitions between solid, liquid, and gaseous states and are often accompanied by significant heat transfer. In these processes, heat is either absorbed or released depending on the direction of the phase transition.
For example, boiling water in a kettle is an endothermic process as it requires continuous heat absorption to transition from liquid to gas (steam).
In contrast, freezing, which is the transition from liquid to solid, would release heat, characterizing it as an exothermic process.

• Boiling: absorbs heat to form gas
• Freezing: releases heat to form solid
• Importance of heat transfer in state transitions