Question

You place hot metal into a beaker of cold water. a. Eventually what is true about the temperature of the metal compared to that of the water? Explain why this is true. b. Label this process as endothermic or exothermic if we consider the system to be i. the metal. Explain. il. the water. Explain.

Short answer

a. The temperature of the metal and water eventually becomes the same, reaching thermal equilibrium. This is because heat transfer occurs from the hotter metal to the cooler water due to the temperature difference, conserving the total energy in the system. b.i. For the metal, the process is exothermic as it loses heat energy to the cold water, resulting in a decrease of its temperature. b.ii. For the water, the process is endothermic as it gains heat energy from the hot metal, resulting in an increase of its temperature.

Step-by-step solution

a. Final Temperature of Metal and Water

When the hot metal is placed into the beaker of cold water, heat is transferred from the metal to the water due to the difference in temperature. The metal loses heat, causing its temperature to decrease, while the water gains heat, causing its temperature to increase. This process continues until the temperature of the metal and water becomes equal, achieving a state of thermal equilibrium. This happens because heat transfer always occurs from a region of higher temperature to a region of lower temperature, in order to minimize the temperature difference and reach a stable state.

a. Explanation for Final Temperature

The reason why the temperature of the metal and water eventually becomes the same is due to the principle of conservation of energy. The heat lost by the metal must be equal to the heat gained by the water. This ensures that the total energy in the system remains constant. As a result, the temperature difference between the two decreases until it reaches zero, at which point no more heat transfer occurs, and the system is in thermal equilibrium.

b.i. Process for the Metal

Considering the hot metal as our system, we observe that it loses heat to the surrounding cold water. Since the metal is losing heat energy, this process is classified as an exothermic process. In an exothermic process, a system releases energy to its surroundings in the form of heat.

b.i. Explanation for the Metal

The process is exothermic for the hot metal because it loses heat energy to its surroundings (the cold water), causing its temperature to drop. This heat transfer occurs due to the temperature difference between the metal and the water, which drives the heat flow from the hotter metal to the cooler water in order to reach thermal equilibrium.

b.ii. Process for the Water

Considering the cold water as our system, we observe that it gains heat from the hot metal immersed in it. Since the water is gaining heat energy, this process is classified as an endothermic process. In an endothermic process, a system absorbs or gains energy from its surroundings in the form of heat.

b.ii. Explanation for the Water

The process is endothermic for the cold water because it gains heat energy from its surroundings (the hot metal), causing its temperature to rise. This heat transfer occurs due to the temperature difference between the water and the metal, which drives the heat flow from the hotter metal to the cooler water in order to reach thermal equilibrium.

Key concepts

Heat Transfer

Heat transfer is a fundamental concept in thermodynamics, describing the movement of thermal energy from a hotter object to a cooler one. In our exercise, this is demonstrated when hot metal is submerged in cold water. Before long, heat begins to flow from the metal to the water. This occurs because heat energy naturally wants to spread out and minimize temperature differences.
When the metal and water begin at different temperatures, they will naturally exchange heat. The metal, initially at a higher temperature, transfers thermal energy to the cooler water. This transfer continues:

• from higher to lower temperature to achieve balance,
• until the temperature of both substances equalizes,
• reaching a condition known as thermal equilibrium.

By the end, the energy lost by the metal equals the energy gained by the water. This is a perfect example of heat transfer leading to thermal equilibrium.

Exothermic Process

An exothermic process is one where energy leaves the system and enters the surroundings. This type of reaction releases heat. Looking at our situation with metal and water, if we take the metal as the system, we find it participating in an exothermic process.
The metal, starting at a high temperature, loses heat to the water. Here's what happens step-by-step:

• The metal releases thermal energy as it cools down,
• This release leads to a drop in the metal's temperature,
• Meanwhile, the surrounding water absorbs this released energy.

This describes the metal's role in an exothermic process because it is losing heat to the water, resulting in a decrease in its own thermal energy but helping to equilibrate the system.

Endothermic Process

Conversely, an endothermic process is when a system absorbs energy from its surroundings. This time, let's consider the cold water as our system. In this context, the process is endothermic because the water absorbs heat.
This absorption leads to the following:

• The water draws in thermal energy from the metal,
• This intake causes the temperature of the water to rise,
• It continues until the water reaches the same temperature as the metal.

As the water gains heat, it is an excellent representation of an endothermic process. In this case, the water's temperature increase demonstrates how it absorbs the energy being released by the cooling metal, achieving thermal equilibrium with its surroundings.