Chemical Energetics Flashcards
(18 cards)
What is an exothermic reaction?
A reaction that gives out energy, usually heat.
What is an endothermic reaction?
a reaction that takes in energy, usually decreases the temperature.
What color does anhydrous copper(II) sulfate turn into?
white → blue
What is a reaction pathway diagram?
graphical representations of the energies that could occur as a reaction progresses to change reactants into products.
What is a neutralisation reaction?
A reaction between an acid and a base/ alkali to produce a neutral salt and water.
What is enthalpy change?
The difference in energy between reactants and products. Units in kJ/mol with symbol ΔH
What is the enthalpy change in exothermic reactions?
–ΔH
represented on pathway diagram with an downwards arrow.
What is the enthalpy change of endothermic reactions?
+ΔH
represented on pathway diagram with an upwards arrow.
What is bond energy?
the amount of energy in kJ/mol that is needed to break one mole of a bond.
How do you calculate the energy change of ΔH
ΔH = energy of bonds broken - energy of bonds formed
What are examples of exothermic reactions?
- combustion
- neutralisation of acid
What are examples of endothermic reactions?
- electrolysis
- melting ice
What is activation energy?
the minimum amount of energy that is needed to start a reaction.
Where are the placements of the reactants and products in an exothermic reaction pathway diagram?
- Reactants are higher
- Products are lower
Where are the placements of the reactants and products in an endothermic reaction pathway diagram?
- Reactants are lower
- Products are higher
Describe enthalpy change.
The enthalpy change, ΔH of a reaction is the transfer of thermal energy during a reaction.
The enthalpy change, ΔH of an exothermic reaction is negative.
The enthalpy change, ΔH of of an endothermic reaction is positive.
How does a chemical reaction occur?
Bonds are broken in the reactants and bonds are made in the products.
- for bonds to break, energy needs to be taken from surroundings (endothermic)
- for bonds to form, energy is released into the surroundings (exothermic)
How do you calculate the enthalpy change of a reaction using bond energies?
- Add up the bond energies for every bond in the reactants
- Add up the bond energies for every bond in the products
- Use ΔH : Energy In - Energy Out
