Question

Which of the following statements is(are) true? a. Energy is changed in form in a process, but it is not produced or consumed. b. Heat is a flow of energy between two objects due to a temperature difference in the two objects. c. In an exothermic reaction, energy as heat flows out of the system into its surroundings. d. In an endothermic process, energy as heat flows from the surroundings into the system.

Short answer

All four statements (A, B, C, and D) are true. Statement A is consistent with the law of conservation of energy, statement B is consistent with the definition of heat, statement C is true for exothermic reactions, and statement D is true for endothermic processes.

Step-by-step solution

Understanding Statement A

Statement A says that energy is changed in form in a process, but it is not produced or consumed. This statement is consistent with the law of conservation of energy, which states that energy cannot be created or destroyed, only converted from one form to another. Therefore, statement A is true.

Understanding Statement B

Statement B states that heat is a flow of energy between two objects due to a temperature difference in the two objects. This statement is consistent with the definition of heat. When there is a temperature difference between two objects, energy in the form of heat transfers from the hotter object to the cooler object until they reach thermal equilibrium. So, statement B is true.

Understanding Statement C

Statement C states that in an exothermic reaction, energy as heat flows out of the system into its surroundings. This statement is also true. An exothermic reaction releases energy in the form of heat, meaning that energy is transferred from the system, which contains the reactants, to the surroundings.

Understanding Statement D

Statement D says that in an endothermic process, energy as heat flows from the surroundings into the system. This statement is in line with the definition of an endothermic process. In an endothermic process or reaction, energy is absorbed by the system from its surroundings in the form of heat. Therefore, statement D is true. In conclusion, all four statements (A, B, C, and D) are true.

Key concepts

Energy Transformation

The idea of energy transformation is central to understanding how energy works in physical systems. It's based on the law of conservation of energy, which posits that energy cannot be created or destroyed, only changed from one form to another. Think of energy as an adaptable traveler, changing vehicles but never disappearing. For instance, in a light bulb, electrical energy transforms into light and heat energy.

Imagine pedaling a bicycle—the mechanical energy from your muscles converts to kinetic energy, propelling the bike forward, and some to heat due to friction. Such transformations are pervasive in everyday life and technologies, reinforcing that energy is consistent and reliable, though it may wear many different 'hats' during its existence.

Heat Transfer

Visualize two cups of coffee, one piping hot and the other at room temperature. Heat transfer is like an invisible hand that moves energy from the hot cup to the cooler surroundings until both become the same temperature. Technically, this is the flow of energy spurred by a temperature difference. This energy movement isn't random—it follows rules, like always traveling from warmer to cooler areas, never the reverse. It continues until thermal equilibrium is reached, meaning both objects share the same temperature.

There are three main modes of heat transfer: conduction (touch), convection (fluid movement), and radiation (waves). Diverse as they are, they all embody the natural tendency of energy to spread out and balance the scales.

Exothermic Reaction

An exothermic reaction is like a mini volcanic eruption releasing energy into its surroundings. It's a process that characterizes many chemical reactions, where the energy stored in chemical bonds is liberated, usually as heat. This outflow of energy can be felt, for example, when hand warmers heat up—it's the heat from an exothermic chemical reaction warming your fingers.

In more scientific terms, if we were to measure the energy before and after such a reaction, we'd find the products are lower in energy than the reactants, with the 'lost' energy having been given off to the environment. This makes these reactions typically heat-producing and often self-sustaining once they begin.

Endothermic Process

Opposite to the fiery release of an exothermic reaction, an endothermic process is like a sponge soaking up heat. These procedures require energy, drawing it in from their surroundings, to proceed. A classic example is photosynthesis in plants, where sunlight (energy) is captured to turn carbon dioxide and water into glucose.

In terms of feel, if you were to touch the surroundings of an endothermic process, it might feel cooler, because energy in the form of heat is being absorbed into the system. To sum up, these processes are marked by their consumption of energy, leading to products that are higher in energy than the reactants. This 'energy hunger' can only be satisfied by absorbing heat from the environment, making the area around colder.