C7-Energy Changes Flashcards
Activation energy
The minimum energy needed for a reaction to take place
Bond energy
The energy required to break a specific chemical bond
Endothermic
A reaction that takes in energy from the surroundings, causing the temperature of the surroundings to decrease e.g.thermal decomposition, the reaction between citric and sodium hydrogen carbonate (sodium bicarbonate)
Exothermic
A reaction that transfers energy to the surroundings which often leads to an increase in temperature as a result e.g. combustion, neutralisation and oxidation
Reaction profile
The relative difference in the energy of reactants and products
Catalyst
Can increase reaction rates by increasing the likelihood of successful collisions, they achieve this by weakening the bonds lowering the activation energy, they do this by providing a alternative pathway and in the process so it is cheaper by using it as they are not used up
Collision theory
Collisions between reacting particles are required for chemical reactions to take place, these collisions must have sufficient energy (activation energy), we can increase the rate of a reaction by increasing the frequency (number)of collisions and/or the energy of reactant particles this can be achieved by changing lots of different factors
Bond breaking
Needs heat energy, is an endothermic process
Bond making
Releases heat energy, is an exothermic process
What sort of reaction is occurring inside a ice pack for physical injuries and why does this lead to the ice pack cooling down
The reaction occurring inside the ice pack is an endothermic reaction. Endothermic reactions absorb energy from the surroundings which means that the temperature of the surroundings decrease.
Conservation of energy
In chemical reactions energy is not created or destroyed, it is conserved and transferred between objects
Hand warmers
Exothermic reaction
Disposable hand warmers use the energy released by iron oxidation
Reusable hand warmers source their energy from the crystallisation of salt solutions. Boiling the pack re-dissolves the crystals so that it’s ready to be activated once more
Sports injury packs
Endothermic reaction
When squeezed forcefully, ammonium nitrate and water mix in the pack resulting in instant cooling
The speed of this reaction makes these packs ideal for scenarios when ice is not immediately available
Reacting profiles
Show the progress of reaction on the x axis and energy level on the y axis they contain the following info:
The relative energies of reactants and products, the activation energy of a reaction, the overall energy change of a reaction
How to calculate bond energy that shows overall energy change energy and strength of chemical bonds
Total bond energies of the reactants minus the total bond energies of the products we can see if a reaction is endothermic or exothermic ,measured in (kJ/mol)
