In the world of chemistry, reactions that release energy to their surroundings fall under exothermic. These reactions are not only fascinating but are also incredibly important, as they play a vital role in various natural and industrial processes.
Knowing how to identify these reactions becomes important for learning more about how chemicals interact. So, let’s explore what defines this kind of reaction, what examples can be observed, and how they can be applied to everyday life.
In this post:
Key Takeaways
Exothermic reactions release energy as heat to their surroundings
These reactions are fundamental to understanding energy transfer and conservation
Bond rearrangements in exothermic reactions are stronger than the original bonds in the components
Common examples of this process include epoxy resin curing, quicklime reacting with water, and cement setting
Exothermic reactions are widely applied in industrial processes like metal extraction and ammonia production
How Do Exothermic Reactions Work?
Definition and Basic Principles
Scientifically speaking, an exothermic reaction is a reaction with a negative enthalpy change, otherwise written as ΔH<0. In simpler terms, an exothermic reaction is when energy from the reacting chemicals transfers to the surroundings, increasing the temperature.
In scientific terms, bonds are broken and reformed during a reaction, and in exothermic reactions, this bond rearrangement results in a net release of energy. When molecules or atoms rearrange to form new bonds, the process can either require or release energy.
In exothermic reactions, the new bonds formed are stronger than those of the components before, releasing the excess energy to the surroundings. The amount of heat released depends on the substances involved and the reaction conditions, which is why some exothermic reactions are mildly warm, while others can cause intense heat.
Common Examples of Exothermic Reactions
It’s always easier to grasp a concept with practical examples, and exothermic reactions are no different. Here’s some that make up a common part of industrial chemistry and processes you may not have considered before.
Epoxy Resin
Epoxy resin, used in adhesives, coatings, and structural materials, undergoes an exothermic reaction when mixed with a hardener. This reaction generates heat, enabling the resin to cure and solidify.
It is a process that requires a lot of control and observation to prevent excessive heating, especially in large scale use. The heat from the curing process helps strengthen the resin, making it durable and adhesive.
Quicklime
Quicklime, or calcium oxide, reacts with water in a strongly exothermic reaction to form calcium hydroxide. When quicklime is added to water, it generates intense heat, often enough to cause the mixture to boil and steam.
This reaction is commonly used in construction to create materials that can set and harden effectively, such as in steel production. The heat produced helps in killing bacteria, which makes it particularly useful in waste management and water treatment.
Cement setting
While it may be surprising, cement setting is another exothermic process. As cement mixes with water and forms a hard mass, this hydration reaction releases heat, which strengthens the cement and speeds up the curing process.
In large cement pours, such as in building foundations or roads, this heat needs to be managed to prevent thermal cracking. The exothermic nature of cement setting is essential for its durability, ensuring long-lasting structures.
What Are the Applications of Exothermic Reactions?
Industrial and Chemical Manufacturing
In industrial manufacturing, exothermic reactions play a crucial role in processes like metal extraction, refining, and chemical synthesis.
Many metal ores, for example, require high-temperature reactions to extract pure metals and refine the end product in a process called metallurgy. The exothermic reactions involved can sustain these conditions, which makes processes more energy-efficient.
Another example is the Haber-Bosch process, which combines nitrogen and hydrogen with a catalyst (usually iron-based) to produce ammonia. This process is exothermic and requires precise temperature management to maximise yield.
Everyday Examples
While we’ve gone over some bigger examples beforehand, there are some smaller scale versions that we take for granted in daily life. Here are two you may not have considered before:
- Combustion – Whether spontaneous or deliberate, combustion gives off a huge amount of heat from the reaction. This can happen in piles of organic material, such as hay, leaves, or coal, where oxidisation slowly works its way through and heat becomes trapped in the layers. With enough heat, the items combust, leading to smoke and fires.
In a more controlled manner, we see combustion in water heaters around the country, often using natural gas as fuel and giving out heat that is captured by water, helping with warming our homes through colder months..
- Hand Warmers – Disposable hand warmers are made of a mixture of iron powder, salt, activated charcoal, distilled water, and vermiculite, these little bundles of heat work through rapid oxidation, with oxygen reacting with the iron, water and salt.
Reusable ones, however, are made of a supersaturated sodium acetate solution, which crystallises and releases heat.
How Are Exothermic Reactions Different from Endothermic Reactions?
While exothermic reactions give off heat, endothermic reactions absorb it, causing a cooling effect to the surrounding area. This happens due to the energy needed to break bonds in the reactants being more than the energy released when new bonds are made.
One of the simplest examples of an endothermic reaction is the process of photosynthesis, where plants use energy from sunlight to turn carbon dioxide and water into oxygen, which is expelled, and glucose, which fuels the plant’s continued growth. This is a vital part of understanding biochemistry, and helps scientists research and study the differences between this and biochemical engineering.
In contrast, in an exothermic reaction, the energy flows outward rather than inward, making exothermic and endothermic reactions complementary in terms of energy dynamics.
Conclusion
Exothermic reactions show how chemistry can transform the world, one reaction at a time. By releasing energy to their surroundings, exothermic reactions drive everything from warming our hands on a chilly day to fuelling industrial production.
Exothermic does not stand alone, however – endothermic reactions play an equal and opposite part in the world of chemical reactions, and to understand one fully is impossible without knowing the other. Still, there’s no doubting the importance of understanding exothermic reactions, and the impact they have on day-to-day life.
