Chemical reactions can change energy in two main ways: they can either give off heat or take in heat. We call these reactions exothermic and endothermic. Let’s explore what these terms mean.
Exothermic reactions are those that release heat into the environment. This happens when the total energy of the products (what’s made) is less than the energy of the starting materials (the reactants). When new bonds form in the products, energy is set free.
Examples of Exothermic Reactions:
Burning Fuels: When things like methane (a kind of gas) burn, they create lots of energy. For example, when methane combines with oxygen, it produces carbon dioxide and water, plus heat. Burning fuels gives off a lot of heat, usually between 30 to 42 megajoules per kilogram, depending on the type of fuel.
Breathing: Living things, including humans, produce energy when they breathe. This process, called cellular respiration, takes a sugar called glucose and combines it with oxygen to make carbon dioxide and water, while releasing energy needed for our bodies to work.
Endothermic reactions, on the other hand, absorb heat from their surroundings. In these reactions, the total energy of the products is higher than that of the reactants. This means they need energy input to help form new bonds in the products.
Examples of Endothermic Reactions:
Photosynthesis: Plants take in sunlight to turn carbon dioxide and water into glucose and oxygen. They absorb around 2800 kilojoules of energy for every mole of glucose produced. This energy is essential for plants to grow.
Dissolving Salts: Some salts, like ammonium nitrate, cool down when they dissolve in water. This is why they're often used in instant cold packs for injuries.
Every chemical reaction, whether it's exothermic or endothermic, needs a starting push known as activation energy. This is the energy needed to break the bonds of the reactants so new bonds can form in the products.
Why Activation Energy Matters:
Exothermic: These reactions release heat. For example, burning fuels and breathing out energy. They usually make more stable products.
Endothermic: These reactions take in heat. For instance, photosynthesis and dissolving salts. They need a continuous energy supply.
Understanding these ideas can help us learn why different reactions behave differently and how energy plays a key role in chemical changes.
Chemical reactions can change energy in two main ways: they can either give off heat or take in heat. We call these reactions exothermic and endothermic. Let’s explore what these terms mean.
Exothermic reactions are those that release heat into the environment. This happens when the total energy of the products (what’s made) is less than the energy of the starting materials (the reactants). When new bonds form in the products, energy is set free.
Examples of Exothermic Reactions:
Burning Fuels: When things like methane (a kind of gas) burn, they create lots of energy. For example, when methane combines with oxygen, it produces carbon dioxide and water, plus heat. Burning fuels gives off a lot of heat, usually between 30 to 42 megajoules per kilogram, depending on the type of fuel.
Breathing: Living things, including humans, produce energy when they breathe. This process, called cellular respiration, takes a sugar called glucose and combines it with oxygen to make carbon dioxide and water, while releasing energy needed for our bodies to work.
Endothermic reactions, on the other hand, absorb heat from their surroundings. In these reactions, the total energy of the products is higher than that of the reactants. This means they need energy input to help form new bonds in the products.
Examples of Endothermic Reactions:
Photosynthesis: Plants take in sunlight to turn carbon dioxide and water into glucose and oxygen. They absorb around 2800 kilojoules of energy for every mole of glucose produced. This energy is essential for plants to grow.
Dissolving Salts: Some salts, like ammonium nitrate, cool down when they dissolve in water. This is why they're often used in instant cold packs for injuries.
Every chemical reaction, whether it's exothermic or endothermic, needs a starting push known as activation energy. This is the energy needed to break the bonds of the reactants so new bonds can form in the products.
Why Activation Energy Matters:
Exothermic: These reactions release heat. For example, burning fuels and breathing out energy. They usually make more stable products.
Endothermic: These reactions take in heat. For instance, photosynthesis and dissolving salts. They need a continuous energy supply.
Understanding these ideas can help us learn why different reactions behave differently and how energy plays a key role in chemical changes.