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Flashcards in Module 5 Deck (13):

How is energy moved in chemical reactions?

Chemicals store amount of energy, differeent chemicals store different amounts. If products of reaction store more energy than original ractants, then must have taken in difference in energy between products and reactants from surroundings during reaction. If store less, then excess energy transferred to surroundings during reacton. overall amount of energy doesn't change. Because energy is conserved in reactions, can't be created or destroyed, only move around.


What is an exothermic reaction?

Transfers energy to surroundings usually by heating, shown in rise temperature. E.g. burning fules-combustion. Many oxidatoin ae endothermic e.g. water releasing energy. Energy released causes sodium to move to surface of water as oxidised.


What is an endothermic racton?

takes in energy, fall in temperature. Les common between citric acid and sodium carbonate. Thermal decomposition, heating substance causes to decompose


How can you measure energy transfer?

Taking temperature of reagents, mixing in polystyrene cup, meausure temperature of solution at end of reaction. Problem with energy meausurments, is amount of energy lost to surroundings. Can reduce by putting polystyrene cup into cotton wool beaker-more insulation put lid on reduce energy loss by evaporation. Method works for neutralisation reactions, or reactions between metal and acids, or carbonates and acids. Can also use method to investigate variables have on amount of energy transferred.


What is the graph for exothermic reactions?

Product are at lower energy than reactants. Difference in height represents overall energy change in reaction. Initial rise in energy represents energy needed to start reaction-activation energy. Activation energy is minimum amount of energy reactants need to colide with each other and react. Greater activation energy, more energy needed to start reacton can be supplied by heating.


What is the graph for endothermic reactions?

Products at higher energy than reactants. Difference in height represents overall energy change during reaction per mole.


What happens in endothermic and exothermic to form new bonds?

Energy supplied=endothermic process.
energy released=exothermic process. In exothermic reactions energy released by formin new bonds is greater than energy needed to break them. Endothermic reactions energy used to break bonds is graqter than energy realeased by forming them.


What are bond energy calculations?

Every chemical bond has particular bond energy associated with it. Bond energy varies slightly depending on compound the bond occurs in.


How do you figure out bond energy calculations?

Can use known bond energies to calculate overall energy cahnge fo raction. Overall energy change is sum of energies needed to braek bonds in reactants minus energy released when new bonds are formed in products.


What chemical reactions hapen in a cell to produce electricity?

2 electrodes must conduct electricity, so are using metals. electrolyte is lliquid that contains ions which react with electrodes. Chemical raction between electrodes and electrolyte set up charge difference between electrodes. If elelctrodes are connected by wire, charge is able to flow and electricity is produced. Voltmeter can also be connected to circuit to measure voltage of the cell.


What does the voltage of a cell depend on?

Differebt metals will react differently with same electrolyte-causes charge difference, or voltage of cell. Type of electrodes used will affect voltage of cell. Can predict voltage of cell might be from information about voltage of other cells. Electrolyte used in cell will alos affect size of voltage since different ions in solution will react differently with metal electrodes used. Battery formed by connecting 2 or more cells together in series. Voltages of cells in battery are combined so is a bigger voltage overall.


What happens with non-rechargable batteries with the used up retants?

In some cells, the chemical reactions that happen at electordes are irrevrsible. Over time reacting particles-ions in electrolyte and metal ions on electrode get used up and turned into products of reaction. Once any one of reactants is used up reaction can't happen and so no electricity is produced. Products can't be turned back into reactants, so cell can't be recharged.


What happens to make a cell rechargable?

reactoin is reversed by connecting it to an external electric current.