energy changes-paper 1 Flashcards
What is a chemical store?
.certain amount of energy - and different chemicals store different amounts.
What is energy conservation?
can’t be created or destroyed, only moved around.
Exothermic and an 2 examples?
.transfers energy to the surroundings,
.COMBUSTION.-burning fuels
.Neutralisation reactions (acid + alkali)
Exothermic reactions 2 everyday uses?
.hand warmers- exothermic oxidation of iron in air (with salt solution catalyst) release energy.
.Self heating cans of hot chocolate and coffee
Endothermic Reaction 2 examples?
.takes in energy from the surroundings.
.Thermal decomposition - heating calcium carbonate causes decompose into calcium oxide+ carbon dioxide:
Endothermic reactions 1 uses?
.sports injury packs - the chemical reaction allows the pack to become instantly cooler
How can Energy Transfer can be Measured? RP
1)Put 25 cm3 of 0.25 mol/dm hydrochloric acid and sodium hydroxide separate beakers.
2) Place beakers in a water bath set to 25 °C
3) Add HCI followed by sodium hydroxide to a polystyrene cup with a lid cotton wool
4) Take temperature mixture 30 seconds, record highest temperature.
5) Repeat steps 1-4 using 0.5 mol/dm increasing hydrochloric acid.
-higher concentration= contains more particles speeds up rate of reaction
1)Energy transferred (with the polysterin cup and acid concentrations) dependent, control and independent variable?
2)what happens when you get an annaomile?
3)How should bar charts be laid out?
1)
Dependent- temperature change
Independent- volume of sodium hydroxide
Control variables- concentrations of acid or volume
2)
-when working out mean exclude Anamolies
3)
-bar charts= don’t Touch Bars next each other not the same
Assessing how good data is? Validity, repeatability, reproducibility, precision?
Validity= the variables are controlled
Repeatability= the exact same person and equipment is used getting the same result
Reproduceability= diffrent methods or a diffrent person
Precison= the resolution of equipment e.g thermometer
Higher resolution-=more accurate
E.g digital thermometer
What is a hydrogen and oxygen fuel cells?
.electrochemical different types of fuel cells, using different fuels +different electrolytes.
=fuel cell combines hydrogen and oxygen to produce nice clean water and release energy.
How do Reaction Profiles Show Energy Changes?
.diagrams that show the relative energies of the reactants and products in a reaction energy changes over the course of the reaction
What is activation energy and initial rise?
.minimum amount of energy the reactants need to collide with each other and react.
=greater the activation energy, the more energy needed to start the reaction -has supplied,
.initial rise= represents the energy needed to start the reaction.
Exothermic reaction graph?
.products lower energy than the reactants.
. difference represents the overall energy change in the reaction the energy given our per mole.
endothermic reaction graph?
.Produce are at a higher energy than the a reactants The difference in height represents the overall
energy change during the reaction (the energy taken in per mole)
What is an electrochemical/chemical cell?
What and Why does the Chemical Reactions in a Cell Produce Electricity (method)?
What can be used to measure the voltage?
=basic system made up of two different electrodes in contact with an electrolyte
-chemicals are converted into electricity
1) Two electrodes conduct electricity-metals.
2) electrolyte is a liquid-contains ions react electrode
3) chemical reactions=electrodes electrolyte =charge difference between electrodes.
4) electrodes connected by a wire, charge is able flow= electricity
=voltmeter can also be connected to the circuit to measure the voltage of the cell.
What factors does Voltage of a Cell Depends on? 3 reasons and explain them
1)Different metals react differently with the same electrolyte=causes voltage difference
2)bigger difference reactivity electrodes, bigger voltage cell.
3)electrolyte used cell= different ions solution react differently with metal electrodes used.
How are battery formed?
(Electrochemical cell)battery is formed by connecting two or more cells together in series. voltages of the cells in the battery
are combined so there is a bigger voltage overall.
Why does in Non-Rechargeable Batteries the Reactants Get Used Up and what is the process? 4
1)chemical reactions at electrode irreversible.
2) reacting particles - ions in the electrolyte metal ions on electrode - used up=turned products
3) Once any one of the reactants is used up, reaction can’t happen= no electricity i
4) products can’t be turned back into the reactants, cell can’t be recharged.
Describe rechargeable and non-rechargeable cells?
Rechargeable - chemical reactions are reversed when an external current is supplied
Non-rechargeable - reactants are used up, cannot be recharged
What determines the voltage obtained from a cell?
2
Types metals used as electrodes
Type and concentration of an electrolyte.
State the advantages and disadvantages of using batteries over cells?
Produces a bigger voltage
1)what is a non recarhgable battery and what is an example?
2)what is a rechargeable battery?
1)Non-rechargeable batteries, e.g. alkaline batteries
-irreversible reactions-cells
-one of the reactants is used up, no produce any more charge replace.
rechargeable cell
-reversed by connecting it to an external electric current.
-Electrical current running in the opposite direction
Adv: prevents the need for disposing toxic chemicals and prevents the extraction of rare elements
Fuel Cells Use Fuel and Oxygen to Produce Electrical Energy? 3
1)=cell supplied with a fuel+oxygen (or air)=uses energy reaction between them=produce electrical energy=produce
voltage continuously.
2) fuel enters cell it becomes oxidised=potential difference within the cell.
3) oxygen to oxidise fuel to generate electricity.
What happens in a chemical reaction? 3
Chemical reactions, old bones are broken, new are formed
1. Energy supplied, breaks existing bonds, endothermic
2. Energy released new bonds are formed exothermic.
