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exothermic and endothermic reactions & bond energy (exothermic…
exothermic and endothermic reactions & bond energy
energy is moved around in chemical reactions
2)if the product of a reaction store more energy that the original reactants then they must have taken in the difference in energy between the products and reactants from the surroundings during the reaction
3)but if they store less then the excess energy was transferred to the surroundings during the reaction
1) chemical store a certain amount of energy and different chemical store different amounts
4) the overall amount of energy doesn't change this is because energy is conserved in reactions it cant be created or destroyed only moved around
exothermic reaction
2) neutralisation reaction are also exothermic
3)many oxidation reaction are exothermic for example adding sodium to water releases energy o it must be exothermic
1) the best example of an exothermic reaction is burning fuels also called combustion this gives out a lot of energy its very exothermic
AN EXOTHERMIC REACTION IS ONE WHICH TRANSFERS ENERGY TO THE SURROUNDNGS USUALLY BY HEATING THIS IS SHOWN BY A RISE IN TEMP
4) exothermic reactions have lots of everyday uses for example
some hand warmers use the exothermic oxidation of iron in air to release energy
self heating cans of hot chocolate and coffee also rely on exothermic reactions between chemicals in their bases
endothermic reaction heat is taken in
endothermic reactions are much less common than exothermic reactions but they include
the reaction between citric acid and sodium hydrogen carbonate
thermal decomposition heating calcium carbonate causes it to decompose into calcium oxide
endothermic reactions also have everyday use
endothermic reactions are used in some sports injuries packs the chemical reaction allows the pack to become instantly cooler.
AN ENDOTHERMIC REACTION IS ONE WHICH TAKS IN ENERGY FROM THE SURROUNDINGS THIS IS SHOWN BY A FALL IN TEMPERATURE
energy transferred can be measured
3)you can reduce it a bit by putting the polyester cup into a beaker of cotton wool to give more insulation and putting the lid on it to reduce energy lost by evaporation
2)the biggest problem with the energy measurements in the amount of energy lost to the surroundings
4)works for neutralisation reactions or reactants between metals and acids or carbonates and acids
1)you can measure the amount of energy released by chemical reactions by taking the temperature of the reagents mixing them in a polystyrene cup and measuring the temperature of the solution
5)you can also use this method to investigate what effects different variables have on the amount of energy transferred
more on transfer
3)add the HCI followed by the NAOH to a polystyrene cup with a lid
4)take the temp of the mixture every 30 seconds and record the highest temp
2)place the beakers in a water bath set 25.c until they are both at the same temperature (25)
5) repeat steps 1-4 using 0.5 mol/dm3 and then 1 mol/dm3 of hydrochloric acid
1)put 25 cm3 of 0.25 mol/dm3 of hydrochloric acid and sodium hydroxide is separate beaker