C7- energy changes 🥤🌡️

• an exothermic reaction is a reaction that transfers energy from the reacting molecules to the surroundings [usually by heating], so the temperature of the surroundings increases. • think exit= exothermic reaction- heat is given out

• some examples of exothermic reactions are: • combustion [burning] • neutralisation • certain oxidation reactions- [e.g- adding sodium to water, since it releases energy.]

• scientists can represent the energy changes that take place, in reactions by drawing an energy profile diagram. [also known as an energy level diagram]

• the products have got less energy, than the reactants. • This is because energy has been transferred from the reaction, to the surroundings. • ; the difference between the energy of the reactants and the products, tells us the energy that has been released to the surroundings.

• exothermic reactions can be used for: • hand warmers- some hand warmers use the exothermic reaction of iron in air [with a salt-solution catalyst], to release energy.

• exothermic reactions can be used for: • self-heating cans- [e.g- for food and drink. • this is because, self heating cans of hot chocolate and coffee rely on exothermic reactions in their bases]

• endothermic reactions are reactions that take in energy, from their surroundings, so the temperatures of the surroundings decreases [gets colder] • think in= endothermic reaction- energy is taken in.

• some examples of endothermic reactions are: • thermal decomposition- [e.g- heating calcium carbonate, causes it to decompose into quicklime [calcium oxide] and calcium dioxide. • the reaction between citric acid and sodium hydrogen carbonate

• the products have more energy than the reactants, since energy has been taken in from the surroundings. • and the difference in energy between the reactants and the products, tells us the amount of energy that has been taken in by the reaction.

• reactions can only occur, when the particles collide with each other and they have to do that with sufficient energy. • activation energy,is the minimum amount of energy that particle must have in order to react.

• in a reaction profile, the activation energy can be labelled as the energy rising to a peak. • the activation energy is from the reactants, to the peak of the curve.

• exothermic energy changes are shown as negative, because energy has been transferred from the surroundings • and in exothermic reactions, energy is transferred from the chemicals, to the surroundings.

• ; in endothermic reactions, energy is gained from the surroundings, therefore endothermic reactions are seen as positive.

• breaking a chemical bond is endothermic, because it requires energy. • think bendo= b for bonds being broken, and endo for endothermic.

• making chemical bonds is exothermic, since it releases energy. • Think mendo= m for bonds being made, and exo for exothermic

• an energy value tells us the energy required to break a chemical bond. • and every chemical bond, has an energy value.

• bond energy change= sum of bonds broken ➖ sum of bonds formed. • if your answer is negative, the reaction is exothermic; if your answer is positive, the reaction is endothermic.