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Energy Flow and Chemical Reaction

Energy Flow and Chemical Reaction

This lesson aligns with Next Generation Science Standards (NGSS) PS1.B

A system includes matter, energy, and information. When a chemical reaction occurs between the system's inputs and outputs, energy must be transferred. Energy and matter can neither be created nor destroyed. Instead, they can only transform into new forms, move in or move out of the system. To accurately understand a system, one must know the inputs, outputs, the flow of matter, energy, and information through the system. For example, in a thermal power station when the coal is burned, the chemical energy is transformed into heat energy. This heat energy is used to boil water and produce steam. The steam flows into the turbine, which spins the generator to produce electricity. In this article, we will discuss types of energy transfer in chemical reactions.

Types of Energy Transfer
The matter is composed of tiny particles that are in constant motion. When the object is warm, these tiny particles move faster as compared to the cooler object. When thermal energy flows, it always moves from a warmer object to a cooler object. Consequently, the motion of the particles between the objects becomes disturbed. This thermal energy is known as heat. Thermal energy can be transferred between objects in three modes conduction, convection, and radiation.

Conduction is the relocation of energy from one object to another through direct contact. A visible example of conduction is cooking food which involves thermal energy. When a metal cooking vessel is placed on a burner, the heat transfers through the vessel into food. The atoms of the food start moving faster as they gain more thermal energy from a metal vessel. As the atoms move faster, a chemical reaction takes place among the food atoms, and the food is cooked.

Convection is the transfer of thermal energy only in fluids e.g., liquids and gases. The boiling of water on a stove is a common example of convection. In this process, the water molecules at the bottom of the vessel are closest to the stove and gain more thermal energy. They start moving faster and spread out, producing lower-density molecules at the bottom of the vessel. These molecules then move to the top of the vessel. The cooler and denser water molecules take their place at the bottom. The process goes on, causing molecules to sink, warm up, rise, cool down, and sink again.

In radiation, energy does not need any direct contact to transfer. Radiation can transfer heat energy even through empty space. For example, the sun is warming the earth. All thermal energy on earth is derived from the sun. It radiates to the surface of the earth, traveling in the form of electromagnetic radiation, e.g., visible light. Some of this energy is absorbed by the objects present on our planet, while the rest of it is reflected back into space in the form of radiation.

Energy and Chemical Reactions 
Different chemical reactions can also transfer energy from one object to another. Energy plays an important role in a chemical process. In a chemical reaction, matter changes its identity as well as physical characteristics such as size and shape. The energy stored in chemical bonds is transformed into thermal energy. Some chemical processes absorb thermal energy. For example, ice cubes absorb heat from the surroundings and melt into water. Other reactions release energy, e.g., combustion reaction. In this reaction, methane reacts with oxygen. It forms carbon dioxide and water. Combustion reaction releases thermal energy in the form of heat.

The change in thermal energy occurs due to the change in the energy stored in the chemical bonds of the molecules. If a large quantity of water is boiled, the thermal energy released in the form of steam would be higher, and vice versa. All chemical reactions do not transform energy at the same rate. Rather, it depends on the type of chemical reaction.

  • When a chemical reaction occurs, energy must be transferred, i.e., released or absorbed.
  • Thermal energy flows from one object to another in three ways: conduction, convection, and radiation.
  • In conduction, energy is transferred between two objects through direct contact, e.g., cooking food in a metal vessel.
  • Convection is a relocation of thermal energy which only occurs in fluids such as liquids and gases.
  • Radiation is the transfer of energy through electromagnetic waves. No direct contact is needed for energy transfer.

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