Energy changes Flashcards
What do chemicals store
a certain amount of energy
and different chemicals store different amounts
What does it mean if the products of a reaction store MORE energy than the original reactants
they must have taken in the difference in energy between the products and reactants from the surroundings during the reaction
What does it mean if the products of a reaction store LESS energy than the original reactants
-the excess energy was transferrred to the surroundings during the reaction
Why does the overall amount of energy not change
-energy is conserved in reactions
-it cant be created or destroyed only moved around
-so amount of energy in the universe always stays the same
What is an Exothermic reaction
one which transfers energy to the surroundings usually by heating
-shown by a rise in temp
Examples of exothermic reactions
-combustion
-neutralisation reaction
-oxidation reactions
What is combustion
-burning fuels
-gives out a lot of energy so very exothermic
What is a neutralisation reaction
acid+ alkali
What are oxidation reactions
-eg adding sodium to water releases energy so is exo
-the reaction releases energy and the sodium moves about on the surface of the water as its oxidised
Exothermic reactions every day uses
-some hand warmers use the exothermic oxidation of iron in air (with salt solition catalsyt) to release energy
-self heating cans of hot chocolate and cofee also rely on exo between chemicals in their bases
What is an endothermic reaction
-one which takes in energy from the surroundings
-shown by fall in temp
Endo compared with exo
Endothermic reactions are much less common then exothermic
Examples of endothermic reactions
-reaction between citric acid and sodium hydrogencarbonate
-thermal decompostiion
Expand on what is Thermal decomposition
-eg. heating calcium carbonate causes it to decompose into calcium oxide (also called quicklime) and carbon dioxide
Endothermic everyday uses
used in some sports injury packs -the chemical reaction allows the pack to become instantly cooler w/o putting it in the freezer
what are reaction profiles
diagrams that show the relative energies of the reactants and products in a reaction
and how the energy changes over the course of the reaction
Describe an exothermic reaction profile
Describe an endothermic reaction profile
What happens during a chemical reaction
old bonds are broken
new bonds are formed
What kind of process is bond breaking and why
-endothermic process
-as energy must be supplied to break existing bonds
What kind of process is bond formation and why
-exothermic process
as energy is released when new bonds are formed
Describe digram of bond breaking
Describe diagram of bond forming
What happens in exothermic reactions
-the energy released by forming bonds is greater than the energy used to break them
What happens in endothermic reactions
the energy used to break bonds is greater than the energy released by forming them
What does every chemical bond have
-a particular bond energy associated with it
-this bond energy varies slightly depending on the compound the bond occurs in
What is the overall energy change
the sum of the energy needed to break the bonds in the reactants
MINUS
the energy releases when the new bonds are formed in the products
What do u have to know to compare the overall energy changes of reactions
the numerical differences in the bond energies
