Question

Indicate with a plus sign \((+)\) any of these processes that require energy and a negative sign \((-)\) any that release energy. (a) arctic ice melting (d) dry ice changing to vapor (b) starting a car (e) blowing up a balloon (c) flash of lightning

Short answer

(a) +, (b) +, (d) +, (e) +, (c) -

Step-by-step solution

Analyze the Processes - Melting of Arctic Ice

Melting requires heat to change the state of ice to water. Since heat is being absorbed from the environment to melt the ice, this process requires energy.

Analyze the Processes - Dry Ice Changing to Vapor

Dry ice sublimates directly from a solid to gas phase, which requires energy to overcome the molecular forces maintaining solid state; therefore, this process requires energy.

Analyze the Processes - Starting a Car

Starting a car involves initiating chemical reactions within the car's battery and engine, which requires energy, primarily electrical energy from the battery.

Analyze the Processes - Blowing up a Balloon

Blowing up a balloon requires the person to do work (in the physical sense) by expanding the volume of the balloon against atmospheric pressure. This process requires energy from the person.

Analyze the Processes - Flash of Lightning

A flash of lightning is a rapid discharge of electrical energy in the atmosphere which releases energy in the form of light, heat, and sound.

Key concepts

Thermodynamics

Thermodynamics is a branch of physics that deals with the relationships between heat and other forms of energy. It explains how thermal energy is converted to and from other types of energy and how it affects matter.

The melting of Arctic ice, which requires energy to transition from a solid to a liquid state, is an example of thermodynamics in action. It involves the first law of thermodynamics, which deals with the conservation of energy. This law states that energy cannot be created or destroyed but can change forms, as when environmental heat turns ice into water.

Phase Changes

Phase changes are transformations between states of matter, such as solid, liquid, and gas, due to an exchange of thermal energy. Dry ice changing to vapor represents a sublimation process, a phase transition from solid to gas without passing through the liquid state.

This phase change, like melting, requires energy. Depending on the direction of the transition (melting, freezing, vaporization, condensation, sublimation, or deposition), energy is either absorbed or released, illustrating the diverse ways in which energy interacts with matter.

Chemical Reactions

Chemical reactions involve the breaking and forming of bonds between atoms, which requires or releases energy. Starting a car activates such chemical reactions within the battery and engine. While the stored chemical energy in the fuel is converted into mechanical work, the battery provides the initial electrical energy needed to ignite the engine.

This conversion is an integral part of the science of thermodynamics and showcases how chemical and mechanical energies are interconnected.

Work and Energy

Work and energy are closely related concepts in physics: work is the process of energy transfer that occurs when a force makes an object move, while energy is the capacity to do work. Inflating a balloon requires work to be done against the external atmospheric pressure, which demands the transfer of energy from the person to the balloon, causing it to expand.

Electrical Energy

Electrical energy is the presence and flow of an electric charge. A common form of energy transfer, electrical energy can readily be converted into other forms such as heat, light, and motion. The flash of lightning, for instance, is electrical energy rapidly releasing from the cloud to the Earth, generating light and sound—complementary forms of energy that emanate from the electricity discharged.