Endothermic processes

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Endothermic vs Exothermic Processes - Explained

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Key Questions

  • An endothermic process is one that needs to have energy added in order to take place. A simple example of an endothermic process is the melting of ice, because ice doesn't melt unless you put energy into it.

    In fancy mathematical terms, we would say that endothermic processes have a positive ∆H value. This is because the amount of energy that the system has after undergoing the process has increased because energy was added to make it happen.

    In terms that we see every day, endothermic processes are the ones that feel cold when we perform them. That's because these processes are sucking energy out of us when we perform them, making us feel cold.


  • There are two factors that determine whether a reaction will occur:

    Enthalpy (ΔH) is a measure of the amount of heat either gained or lost during a reaction. If a reaction gives off energy (ΔH is negative), the reaction is exothermic and you'll probably feel the energy given off as heat. If a reaction absorbs energy (ΔH is positive), the reaction is endothermic and you'll feel it getting colder as it pulls energy out of your hand).

    Entropy (ΔS), on the other hand, measures the change in randomness that takes place over the course of the reaction. You see, the universe likes for things to become more random, so processes with a positive ΔS value are favored, while those with a negative one are not.

    As a result, reactions occur when the total energy of the system from both entropy and enthalpy decreases. This total energy is called the free energy, and we denote this with the term ΔG. When ΔG is negative, the reaction is spontaneous. If it's positive, the reverse of the reaction will be spontaneous. If it's zero, you've got yourself an equilibrium.

    So, how do we find ΔG? With an equation, of course:
    ΔG= ΔH – TΔS

    If you put your values of enthalpy and entropy into this equation, as well as the temperature, you can figure out if the reaction will occur spontaneously. (One tip: entropy is usually given in Joules rather than kilojoules as enthalpy is given, so divide that term by 1000 before doing the calculation).

    Reference :- http://www.knowswhy.com/why-do-endothermic-reactions-occur/

  • Exothermic processes give off energy (they feel hot). Endothermic processes require energy (they feel cold).

    Here's the deal: Exothermic processes are those that release energy into the environment. For example, when you burn a piece of wood, the reaction is exothermic, meaning that the energy which formerly existed as chemical bonds has been released as heat into the environment. Please note that this doesn't mean the energy has vanished, just that it has turned from bond energy to thermal energy.

    Endothermic processes require energy to take place, so absorb energy from the environment. An example of this is the melting of ice. The reason that melting ice feels cold in your hand is that the energy for this process is being pulled out of your hand, and this loss of energy makes your hand feel cold.