enthalpy changes & energy profiles Flashcards
Where do chemicals store energy?
In their bonds
Define endothermic reactions
Reactions that take in more heat energy from their surroundings than they give out
Describe what an endothermic reaction is in the terms of energy stores in bonds.
If the products (what is produced) in a reaction contain more energy in their bonds than the reactants (what was put in) do, they must have absorbed energy from the surroundings. (Remember: principle of energy: the overall amount of energy doesn’t change)
Define exothermic reactions
Reactions that release more heat energy to their surroundings than they took in
Is breaking bonds an endothermic or exothermic process? Explain.
Endothermic. Energy is needed to break the bonds, so it is absorbed from the surroundings (endo). This is called the activation energy
Is making bonds an endothermic or exothermic process? Explain.
Exothermic. When the new bonds are formed, they release the energy they used to form the bonds (to the surroundings), therefore making it an exothermic process.
What are energy profiles?
Diagrams to show the relative energy’s of the reactants and products in a reaction (how does energy change over the course of a reaction?)
What is the activation energy?
The initial rise in energy, the energy required for the reaction to begin
Describe an exothermic energy profile and explain.
At first, there is an increase of energy, due to the bonds of the reactants being broken (chemical absorbs energy, total enthalpy increases). This is the activation energy, as it is required for the bonds to break and the reaction to begin. But there is a BIGGER drop in energy overall because when the bonds of the products are formed (releasing energy) it is more than the energy required to break the bond, making it an exothermic reaction.
Describe an endothermic energy profile and explain.
Firstly, there is a large energy increase, as the bonds of the reactants break (absorbs a lot of energy). This is the activation energy, and it is larger than an exothermic reactions activation energy, because MORE energy is absorbed to break the bonds than is released when making the bonds, making it an endothermic reaction.
In exothermic and endothermic reactions, when we talk about temperature, what are we measuring the temperature change of?
the surroundings. Ex: exothermic reactions release energy, so the temperature would increase (heat is released energy to surroundings, surroundings gain more energy, increase in temperature)
