Higher: C5 - Energy changes Flashcards
What is an exothermic reaction?
One which transfers energy to the thermal energy store of the surroundings.
Give 3 examples of exothermic reactions.
Combustion, neutralisation and many oxidation reactions.
Give 2 everyday uses of exothermic reactions.
Self-heating cans and hand warmers.
What is an endothermic reaction?
One which takes energy from, and decreases the thermal energy store of, the surroundings.
Give 2 examples of endothermic reactions.
Thermal decomposition, and the reaction between citric acid and sodium hydrogencarbonate.
Give one use of an endothermic reaction.
Sports injury packs.
Describe how you could test the effect of concentration of HCl on the energy released in a neutralisation between HCl and NaOH.
1) Place equal volumes of HCl and NaOH (of equal concentrations) in beakers.
2) Put these in a water bath at a set temperature and wait for them to reach this.
3) To minimise energy lost to the surroundings, line a beaker with cotton wool and put a polystyrene cup inside it.
4) Add the HCl and NaOH to the cup and place a lid on it, recording the starting temperature w/ a thermometer.
5) Record the temperature every 20 seconds until the temperature stops increasing.
6) Repeat steps 1-5 with different concentrations of HCl, and repeat each stage 3 times to find an average.
Is the process of breaking bonds exothermic or endothermic, and why?
Endothermic, because it takes energy to overcome the forces holding together the bonds.
Is the process of forming bonds exothermic or endothermic, and why?
Exothermic, because particles become more stable when they form compounds.
Why do exothermic reactions release energy to the surroundings?
The energy released by forming bonds is greater than the energy used to break them.
Why do endothermic reactions take energy from the surroundings?
The energy used to break bonds is greater than the energy released by forming them.
What is the activation energy of a reaction?
The minimum amount of energy that particles must have to react.
What are reaction profiles?
Diagrams that show the changes in the relative energies of the reactants and products of a reaction. The progress of the reaction is plotted against energy.
Draw a reaction profile for an exothermic reaction.
Draw a reaction profile for an endothermic reaction.
