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Chemistry > C7-Energy Changes > Flashcards

C7-Energy Changes Flashcards

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1
Q

What are Exothermic reactions ?

A

Exothermic reactions transfer energy from the reacting molecules to the surroundings . Thereforre , the temperature of the surroudings increases (hotter ) .

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2
Q

Examples of Exothermic rections .

A

Combustion and certain oxidation and neutralisation reactions .

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3
Q

How do scientists represent energy changes that take place in a reaction ?

A

By drawing an energy profile diagram .

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4
Q

What does star one show for exothermic reaction profile ?

A

Products have less energy that reactants , as energy is being transferred from the reaction to the surroudnings ..

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5
Q

How do we figure out the energy released to the surroudings in an exothermic reaction profile ?

A

The difference between the energy of the reactans and the enrgy of the products tells us the energy released to the surroudnigs .

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6
Q

Label the energy change on the exothermic diagram .

A

.

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7
Q

Wat are tewo uses of exothermic reactions .

A
  • Hand warmers

- Self-heating cans example food and drink .

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8
Q

What are endothermic reactions ?

A

They tae in energy fromt heir surroundings . Thereofore the temperature of the surroundigns decreases (gets colder )
an example i thermal decompostion .

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9
Q

What does star one show for enndothermic reaction profile ?

A

Products have got more energy than reactants . As enegry is being taken in from the surroudnigns .

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10
Q

How do we figure out the energy release taken in from the surroudings in an endothermic reaction profile ?

A

-The difference in energy between the reactants and products , tells us the amount of energy taken in by the reaction .

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11
Q

Similarirites in both endo and oexothermic reactions ?

A

-In both cases eergy rises to a peak . This is the activaiton energy . WHICH ARE THE PEAKS OF THE CURVES , LABEL IT ON ENERGY PROFILE .
-The minimum amount of energy that paricles must have in order to react is called he activation eenrgy .
FROM THE PEAK TO THE CURVE CHECK HE SHEET AND LABEL ON PROFILES .

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12
Q

What is the RQP for invesigating temp chage ?

A
  • Investigating the temperature change in an exothermic reaction .
  • This is a reaction between hydrochloric acid and the alkali sodium hydroxid e.
  • We are going to add incresing volumes of sodium hydroxide solution to hydrochloric acid . In each experiment , will measure the maximum temperature reached .
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13
Q

What is the independant variable ?

A

Volume of sodium hydroixide solution .

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14
Q

What is the dependant variable

A

The maximum temperature reached .

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15
Q

What is the control variable ?

A

VOLUME OF HYDROCHLORIC ACID AND CONCENTRATION OF BOTH SODIUM HYDROIXDE SOLUTION AND HCL .

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16
Q

Stage one for RQP for investigation temp change ?

A

Use a measuring cylinder to measure 30cmcubed of dilute hydrochloric acid .

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17
Q

Stage two for RQP for investigation temp change ?

A

Transefr acid into a polystyrene cup .

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18
Q

Stage three for RQP for investigation temp change ?

A

Stand the polstyrene cup inside a beaker , this stops the cup from falling over .

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19
Q

Stage four for RQP for investigation temp change ?

A

Next we use a thermometer to measure the temperture of the acid and we record this in a table .

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20
Q

Stage five for RQP for investigation temp change ?

A

Now we use a measuring cyclinder to meassure 5cm cubed of sodium hydroxide solution and we transfer this to the polystrene cup .

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21
Q

Stage six for RQP for investigation temp change ?

A

Fit a plastic lid to the cup and plce thermometer through the hole in the lid .
-The bulb of the thermometre must be in the solution

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22
Q

Stage seven for RQP for investigation temp change ?

A

Use the thermometer to gently stir the solutoin .
-Because this reaction is exothermic , it releases energy . This means that the temperature of the solution will increase.

23
Q

Stage eight for RQP for investigation temp change ?

A

Now we look carefully , at the temperature rise , on the thermoemeter .
-When the reading on the thermomeer sops chaning , we record the highest temperature reached .

24
Q

Stage Nine for RQP for investigation temp change ?

A

Rinse out the polstyrene cup . Repea the whole experiemnt using 10cm cubed of sodium hydroxide solution .
-Carry out the experiment severla more times , each tie increading the volume of sodium hydroxide solution b 5cm cubed until we reach a maximum of 40 cm cubed of sodium hydroixde solution

25
Q

Stage ten for RQP for investigation temp change ?

A

Repeat the experiemnt one more time , so e have wo ses of results . Use this to calcualte a mena caue , for maximum temperature reached for each volume of sodium hydroxide soluon .

26
Q

Check the graph for the RQP , what does star one show ?

A

-As we increase the volume of sodium hydroxide solution , the maximum temperature reaced increases .
BECUASE - as we add more particles of sodium hydroxide ,t hey react iwth hydrochloric acid .
-This is an EXOTHERMIC reaction , so more enrgy is releaseed and the maximum temperature reached increases .

27
Q

Check the graph for the RQP , what does star twos hwo ?

A

At a certian volume of sodium hydroxide solution , the maximum temperature reached starts to decrease .

  • At this point we are adding so much sodium hdroxide ,that there is not enough hydrochloric acid . Meaning some of the sodium hydroxide is unable to react .
  • Because of this ,t he amoutn of energy released by the reaciton has reached a maximum .
28
Q

Why does the temperature actually decerase from start two ont he RQP graph ?

A
  • In each experiemnt , we are adding a greater volume of solution .
  • So energy relesed is now spread out into a greater volme .
  • Because of this ,when we dd large volumes of sodium hydroixde solution , the maximum temperature reached decreases .
29
Q

EXAM QESTION - , why are we using a polystyrene cup ith a lid ?

A
  • As we are measuring the temperature in the ecperiment . This means , we want to reduce any heat loss .
  • Polystyrene is a good thermal inslator , reducing heatloss htrough the sides and the botto , and the lid reduces heat loss into the air .
30
Q

What can we do if we ake two different metals and place them into an electrolyte ?

A

-We can produce electricity .

31
Q

What is an electrolyte ?

A

-AN electrolyte is a solution that can doduct electricty , e.g a solution of an ionic compound .

32
Q

Look at the setup on the page ,

what is the setup for a cell ?

A
  • a strip of copper nad magnesium is palced inside an electrolyte soluton .
  • If you connect the two metals with a voltmetre , you cn see a potetntial difference and an electric current will flow through the wire .
  • A chemical reaction is taking place on the surface of the two metals , and these reactions are producing electircity , this setupp is called a CELL .
  • Cells can be used to generate electricity .
33
Q

Facts about a cell

A
  • A cell can only produce electicity for a certian period of time .
  • Eventually the chemicals in the cell runout and the reaction stops .
  • Cells only produce electicity if we use metals with different reactivities .
34
Q

Reactivity and votage ?

A
  • The bigger the difference in reactivity in metals , the larger potential difference produced by the cell .
  • THe electrolyte also affects the potential difference .e
35
Q

A battery

A

-A battery cotins two or mroe cells connected ins eries , to produce a greater voltage

36
Q

Alkaline batteries ?

A
  • In alkaline batteries at some point , the reactants in the batteries run out and no more electricity is produced .
  • There is now way we can reverse these reactions so these are NON - RECHARGEABLE BATTERIES.
37
Q

Rechargeable batteries ?

A
  • Rechargeable batteries can be rechrged .

- As we can reverse the chemical reactions when we apply an electric current .

38
Q

What happens in a fuel cell ?

A
  • We react a fuel (hydrogen) with either pure oxygen or air .
  • Inside the fuel cell ,a chemical reaction reaction takes place , producing an electric current , the only waste prodcut is water .
39
Q

Draw the diagram .

A

:)

40
Q

What happens at the negative electrode of the reaction ?

A

-The hydrogen molecule spilts into hydrogen ions and electrons .
-These electrons pass through the wire and that is the electric current .
See the equation on the page and learn .

41
Q

What happens at the positive electrode of the reaction ?

A
  • Oxygen molecules combine with electrons and hydrogen ions produced at the negative electrode .
  • See equation on the page and learn .
42
Q

TO CONCLUDE , what happens at the hydrogen fuel cell ?

A

-In a hydrogen fuel cells , hydrogen is combined with oxygen (Hydrogen is oxidiised .)
The overal equaion is (check book too )
Nh2+O2—>2H20 (Hydrogen is being oxidised )

43
Q

What is one advantage of hydrogen fuel cells ?

A

Hydorgen fuel cells will produce electricity for AS LONG AS YOU PROVIDE HYDROGEN .

44
Q

What is another advanatage of hydrogen fuel cells ?

A

Hydrogen fuels cellsdo not get less efficent the logner they are run .

45
Q

What is the last advantage of hydorgen fuel cells ?

A

Hydrogen fuel cells can be a source of drinkable water e.g on a spacecraft .

46
Q

What is one disadvantage of a hydrogen fuel cell ?

A

Hydrogen fuel cells runon hydrogen which is an explosive gas and it is very difficult to store safely .

47
Q

What is another disadvanatge of hydrogen fuel cells ?

A

-Hydrogen fuel cells produce a realtively low potential diffeence , or voltage so several are needed together

48
Q

What is one advantage of rechargeable batteries ?

A

-No dangerous fuels are required with rechargeable batteries .
(Some types of rechargeable batteries can catch fire if not manufactured correctly )

49
Q

What is another advantage of rechargeable batteries

A

Rechargeable batteries can produce a greaer potential difference than a hydrogen fuel cell .

50
Q

What is one disadvantage of rechargeable batteries ?

A

-Rechargeable batteries run out , and need to be recharged .

51
Q

What is another disadvantage of rechargeable batteries ?

A

-Rechargeable batteries can store less electricity the more charginc ycles they go through and eventually need replacing so are not that efficent .

52
Q

yay fuel cells

A

-dont produce ppllutants whereas fossil fuels do .
petrolc omesfrom fosilf uels - combustion of that porduces co2 atmosphere .
-fossil fuels re a finite supply , whereas getting hydorgen from water wont run out .

53
Q

hydorgen fuel cells noo

A

Hydrogen is a gas and requires a much larger storage volume compared to fossil fuels like petrol.
no efficent wya to produce hdyorgen , actually still genrared from burnign fosisl fuels .
electrolysis for h ydrogen fuel cells is expensive .,

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