Question

Define these terms: thermochemistry, exothermic process, endothermic process.

Short answer

Thermochemistry studies heat changes in reactions; exothermic processes release heat, while endothermic processes absorb heat.

Step-by-step solution

Define Thermochemistry

Thermochemistry is the scientific study of the energy and heat associated with chemical reactions and/or physical transformations. It considers the exchange of energy, particularly in the form of heat, and how it influences matter during these changes.

Define Exothermic Process

An exothermic process is a type of chemical reaction or physical change that releases heat energy to its surroundings. In exothermic processes, the energy needed to start the reaction is less than the energy released, making the surroundings feel warmer.

Define Endothermic Process

An endothermic process is a chemical reaction or physical change wherein the system absorbs heat energy from its surroundings. In these processes, the energy required to initiate the reaction is greater than the energy released, leading to cooling of the surroundings.

Key concepts

Exothermic Process

In chemistry, an exothermic process is a type of chemical reaction or physical change that emits energy in the form of heat. This energy release usually results in the surroundings feeling warmer. One common example is the combustion of wood in a fireplace. Here’s how the process works:

• During the reaction, bonds in the reactants break, releasing energy.
• The formation of new bonds in the products releases even more energy.
• Overall, the energy released is greater than the energy required to start the reaction.

An interesting aspect of exothermic processes is that they are self-sustaining after initiation, unlike endothermic processes. This means once started, they continue as long as there is reactant available.

Endothermic Process

An endothermic process is a chemical reaction or physical change that requires the absorption of heat from the surroundings. This usually makes the surroundings cooler. A typical example is the melting of ice cubes. Here is the basic mechanism behind it:

• Energy is absorbed to break the bonds in the reactants, such as the hydrogen bonds in ice.
• This energy absorption is crucial as it allows the phase change from solid to liquid.
• In endothermic processes, the absorbed energy is greater than any energy released.

These processes are not self-sustaining. They need a continuous supply of energy from the environment to proceed. Hence, you might need to keep adding heat to the system to maintain the reaction.

Energy Exchange in Reactions

Energy exchange is a critical aspect of chemical reactions, greatly influencing reaction products and feasibility. The fundamental principle lies in the first law of thermodynamics, which states that energy cannot be created or destroyed, but can change forms. In chemical reactions, this involves the transformation between chemical energy and heat.

• In exothermic reactions, energy is transferred from the reactants to the surroundings, typically as heat.
• Conversely, in endothermic reactions, energy is transferred from the surroundings to the reactants.
• The direction and mode of the energy exchange determine whether the reaction feels hot or cool to the touch.

Understanding energy exchange helps predict the spontaneity of reactions. It can indicate how much energy is needed to start a reaction or how much energy will be released. This is especially relevant in applications such as energy-efficient chemical processes and controlling environmental conditions in industries.