energy changes-paper 1

Question 1

What is a chemical store?

Answer 1

.certain amount of energy - and different chemicals store different amounts.

Question 2

What is energy conservation?

Answer 2

can’t be created or destroyed, only moved around.

Question 3

Exothermic and an 2 examples?

Answer 3

.transfers energy to the surroundings,
.COMBUSTION.-burning fuels
.Neutralisation reactions (acid + alkali)

Question 4

Exothermic reactions 2 everyday uses?

Answer 4

.hand warmers- exothermic oxidation of iron in air (with salt solution catalyst) release energy.
.Self heating cans of hot chocolate and coffee

Question 5

Endothermic Reaction 2 examples?

Answer 5

.takes in energy from the surroundings.
.Thermal decomposition - heating calcium carbonate causes decompose into calcium oxide+ carbon dioxide:

Question 6

Endothermic reactions 1 uses?

Answer 6

.sports injury packs - the chemical reaction allows the pack to become instantly cooler

Question 7

How can Energy Transfer can be Measured? RP

Answer 7

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

Question 8

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?

Answer 8

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

Question 9

Assessing how good data is? Validity, repeatability, reproducibility, precision?

Answer 9

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

Question 10

What is a hydrogen and oxygen fuel cells?

Answer 10

.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.

Question 11

How do Reaction Profiles Show Energy Changes?

Answer 11

.diagrams that show the relative energies of the reactants and products in a reaction energy changes over the course of the reaction

Question 12

What is activation energy and initial rise?

Answer 12

.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.

Question 13

Exothermic reaction graph?

Answer 13

.products lower energy than the reactants.
. difference represents the overall energy change in the reaction the energy given our per mole.

Question 14

endothermic reaction graph?

Answer 14

.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)

Question 15

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?

Answer 15

=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.

Question 16

What factors does Voltage of a Cell Depends on? 3 reasons and explain them

Answer 16

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.

Question 17

How are battery formed?

Answer 17

(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.

Question 18

Why does in Non-Rechargeable Batteries the Reactants Get Used Up and what is the process? 4

Answer 18

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.

Question 19

Describe rechargeable and non-rechargeable cells?

Answer 19

Rechargeable - chemical reactions are reversed when an external current is supplied
Non-rechargeable - reactants are used up, cannot be recharged

Question 20

What determines the voltage obtained from a cell?
2

Answer 20

Types metals used as electrodes
Type and concentration of an electrolyte.

Question 21

State the advantages and disadvantages of using batteries over cells?

Answer 21

Produces a bigger voltage

Question 22

1)what is a non recarhgable battery and what is an example?
2)what is a rechargeable battery?

Answer 22

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

Question 23

Fuel Cells Use Fuel and Oxygen to Produce Electrical Energy? 3

Answer 23

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.

Question 24

What happens in a chemical reaction? 3

Answer 24

Chemical reactions, old bones are broken, new are formed
1. Energy supplied, breaks existing bonds, endothermic
2. Energy released new bonds are formed exothermic.

Question 25

What is exothermic and endothermic?
What happen when you break and form bonds?

Answer 25

1-Exothermic energy released, forming bonds, greater energy used to break them.
-Endothermic energy used to break bonds, greater energy released by forming them

Breaking= absorbs energy
Production= releases energy

Question 26

Bond energy calculations? (Energy required)

Answer 26

. Given bond energy’s
.multiply how many bond + add other bonds

Question 27

Overall energy change? (Endothermic and exothermic)

Answer 27

Overall energy change= energy taken in- energy realised

Question 28

How do you hydrogen fuel cells involved a redox reaction? 6 points

Answer 28

1) electrolyte (phosphoric acid) electrodes (porous carbon) with a catalyst.
2) Hydrogen goes into the anode compartment and oxygen goes into the cathode compartment.
3)anode hydrogen loses electrons to produce H* ions. oxidation.+ 4H* ions in the electrolyte move to the cathode. reacting with -OH to create water
5) cathode oxygen gains electrons from cathode and reacts with H+ ions (phosphoric acid electrolyte) to make more -OH
6) The electrons flow through an external circuit from the anode to the cathode - this is the electric current.

Question 29

What happens at the fuel cell in cathode and anode?

Answer 29

Panic is reversed (fuel cells)
-hydrogen lose electrons
-oxygen (reduced) react hydrogen (oxideised) use ions to form h20

Question 30

What are the reactant and products of hydrogen Fuel cells?
How do you get the hydrogen?

Answer 30

Hydrogen fuel cell:
- oxygen and hydrogen
-hydrogen->hydrogen ions (elctroyte)->oxygen reacts water to produce hydroxide ions keeps the cycle going
-hydroxide ion+oxygen=water ( more efficient less loss of heat)

To get hydrogen:
-electrolysis of water (expensive) huge amount energy
-react methane with steam realising co2

Question 31

What is a redox reaction??

Answer 31

Reduction at the cathode, an oxidation at the anode

Question 32

What is the equation to find enthalpy change in terms of bond energies?

Answer 32

Energy of reaction = sum of bonds broken - sum of bonds made

Question 33

What is the overall reaction in a hydrogen fuel cell? What are the half equations?

Answer 33

-overall take all things that are not ions

Question 34

What are the advantages fuel cells vs chemical cells? 8 Hydrogen and 5 for rechargeable

Answer 34

-hydrogen= no pollution
-High pressure tanks are needed to store the oxygen and hydrogen in sufficient amounts which are dangerous and difficult to handle
-No batteries to dispose of which is better for the environment

Question 35

1)What is a simple cell?
2)how is a simple cell set up?
3)describe how it produces an electrical charge?
4) how to create a charge difference?

Answer 35

1)simple cell is a source of electrical energy
2)two electrodes made from metals different reactivity in electrolyte connected external voltmeter wire

3)
1-more reactive metal= forms ions more easily=readily releasing electrons
2-electrons give more reactive electrode a negative=charge difference between the electrodes
3-electrons flow around the circuit least reactive electrode=positive electrode
4-difference ability of the electrodes to release electrons causes a voltage to be produced

4)
5-greater the difference in the metals reactivity then the greater the voltage produced
6-electrolyte used affects voltage as different ions react with the electrodes in different ways

Question 36

alkaline cells 1 pro and 2 cons?

Answer 36

-Cheaper to manufacture

-May end up in landfill sites once fully discharged; recyclable
-expensive

Question 37

1)Fuel cell?
2)cell?

Answer 37

1)Electrical cell supplied with a fuel and oxygen and efficiently transfers energy realised by the reaction as electricity
2)chemicals that react to produce electricity