How to Tell If a Reaction Is Exothermic

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An exothermic reaction is one where an object transfers thermal energy in the form of heat away from itself. In essence, it releases the thermal energy. This occurs in a number of situations, and it can be important to understand whether a reaction is exothermic or not. All chemical reactions include a transfer of energy, and when the reaction occurs, it either absorbs energy or releases it. There is another term called enthalpy, which is the measure of the total energy of a system. The change in enthalpy is usually called the heat that is given off or absorbed during a chemical reaction. Read on to learn how to tell if a reaction is exothermic.

Does it Release Thermal Energy?

An exothermic reaction always releases thermal energy in the form of heat. The heat is released because the total energy of the products is less than the total energy of the reactants. For example, a bonfire is an exothermic reaction. The fire burns, and it releases heat through this reaction. The heat is transferred to surrounding space and air, and it warms it. Another example is when you have a strong acid and place it in water. The acid dissociates quickly and releases heat, causing an exothermic reaction.

Does it Have a Positive or a Negative Enthalpy?

The enthalpy is the total energy or heat that is given off or absorbed during a chemical reaction. In an exothermic reaction, energy is released because the total energy of the products is less than the total energy of the reactants. As a result, the change in enthalpy will always be negative for an exothermic reaction. If a reaction has a negative enthalpy, you can be certain that it is exothermic.

Does the Reaction Require External Energy to Occur?

If the reaction is dependent on external energy that is usually in the form of thermal energy or heat, then it is not an exothermic reaction. An exothermic reaction will release heat, causing the environment around it to grow hotter, whereas an endothermic reaction is dependent on external heat. For example, an ice cube melting is an endothermic reaction that is dependent on air surrounding it to be warmer than the freezing point of water, which is zero degrees Celsius. Because it absorbs heat, it is not an exothermic reaction.

When you want to determine whether a reaction is exothermic, you need to know whether it releases or absorbs energy. There are several different ways to figure this out. In the case of ice melting, it is clear that the ice is absorbing heat energy to cause the melting. That means that it is not exothermic.

If you consider cooking scrambled eggs, you need to know whether the eggs cook because they absorb heat or because they release heat. The chemical reaction that changes the state of the eggs is the result of the eggs absorbing heat. They are not exothermic. However, when you turn the stove on, the heat is transferred from the stove to the pan, and from the pan to the eggs. This means that the stove heating the pan is an exothermic reaction. The pan heating the eggs is as well.

Sometimes it is not possible to know without looking at an equation. In this case, you need to know the enthalpy. If the enthalpy is negative, then the reaction is exothermic because the object is releasing heat. If the enthalpy is positive, then you know that it has absorbed heat and is an endothermic reaction.

Understanding the basics of an exothermic reaction will help you determine whether one has occurred. It is important to understand the process of the transfer of thermal energy, and you can observe this in everyday events, such as cooking, heating your home, and objects reaching a melting point.

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