C7- energy changes 🥤🌡️ Flashcards
What is an exothermic reaction ?
- 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
Name three examples of exothermic reactions ? [3]
Hint: oxidation
- some examples of exothermic reactions are:
- combustion [burning]
- neutralisation
- certain oxidation reactions- [e.g- adding sodium to water, since it releases energy.]
How can scientists represent the energy changes that take place, in reactions ?
- scientists can represent the energy changes that take place, in reactions by drawing an energy profile diagram. [also known as an energy level diagram]
What can you tell me about an exothermic energy profile reaction ?
Hint: less energy
- 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.
How can exothermic reactions be useful in hand warmers ?
- 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.
How else can exothermic reactions be useful in self heating cans ? [1]
- 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]
What are endothermic reactions ?
- 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.
Name two examples of endothermic reactions
- 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
What can you tell me about an endothermic energy profile reaction ?
Hint: more energy
- 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.
What is activation energy ?
- 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.
How can activation energy be labelled, in a reaction profile ?
Hint: energy rising
- 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.
Why are exothermic reactions seen as negative ?
- 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.
Why are endothermic reactions seen as positive ?
- ; in endothermic reactions, energy is gained from the surroundings, therefore endothermic reactions are seen as positive.
Is breaking a chemical bond exothermic or endothermic. Explain your answer
- breaking a chemical bond is endothermic, because it requires energy.
- think bendo= b for bonds being broken, and endo for endothermic.
Is making a chemical bond exothermic or endothermic. Explain your answer
- making chemical bonds is exothermic, since it releases energy.
- Think mendo= m for bonds being made, and exo for exothermic
