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CHEMISTRY > C3 - Chemical Reactions > Flashcards

C3 - Chemical Reactions Flashcards

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1
Q

What happens to mass in a chemical reaction?

A

Is a chemical reaction mass is always conserved.

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2
Q

How do you use RFM to show mass is conserved?

A

Mr of reactants = Mr of products
Q1) Use relative formula mass to show mass is conserved in : 2Li + F2 -> 2LiF

Mr of reactants = (2 x 6.9) + (2 x 19) = 51.8
Mr of Products = (2 x 6.9) + (2 x 19) = 51.8

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3
Q

What happens when mass of reaction changes?

A

A gas has become involved :
If mass increases, gas has been introduced into chemical reaction
If mass decreases, the gas has escaped from unclosed experiment

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4
Q

How do you work out chemical formulas?

A

All charges of compounds are zero, so plus charges must equal negative charges.

Q1) What is the chemical formula for calcium Nitrate?
Ca2+ and No3(-)
Two No3 are required to make 2- hence:
Ca(No3)2 = calcium nitrate

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5
Q

What are the formulas of Water, Ammonia, Hydrogen, Carbon dioxide, Chlorine, Oxygen?

A 
Water = H20
Ammonia = NH3
Hydrogen = H2
Carbon dioxide = CO2
Chlorine = Cl2
Oxygen = O2
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6
Q

How do you balance equations?

A

Make sure there are the same amount of elements on one side of the equation than on the other side.

Eg : H2SO4 + NaOH -> Na2SO4 + H20
H = 3 H = 2
S = 1 S = 1
0 = 5 O = 5
Na = 1 Na = 2

H2SO4 + 2NaOH -> Na2SO4 + 2H20
H = 4 H = 4
S = 1 S = 1
0 = 6 O = 6
Na = 2 Na = 2

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7
Q

What are ionic equations?

A

Ionic equations you only separate (aq)

Q1) Write ionic equation for CaCl2(aq) + 2NaOH(aq) -> Ca(OH)2 (s) + 2NaCl(aq)

Ca(2+) + 2Cl(-) + 2Na(+) + 2OH(-) -> Ca(OH)2 + 2Na(+) + 2Cl(-)

CANCLE OUT
Ca(2+) + 2OH(-) -> Ca(OH)2

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8
Q

What are half equations?

A

Half equations show electron movement

Q1) Show half equation of chloride ions

2Cl(-) - 2e(-) -> Cl2

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9
Q

What is the value of a

Avogadro’s constant?

A

6.02 x 10^23

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10
Q

What does Avogadro’s Constant show?

A

Shows the number of atoms, particles, elements etc in 1 mole of a substance

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11
Q

What is one mole of any element or molecule equal to in terms of mass?

A

One mole = Mr of atom or molecule

Eg: One mole of Carbon = 12g
One mole of Nitrogen gas = 28g

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12
Q

How do you find the mean mass of an atom ?

A

Mass of one atom = Mr / Avogadro’s constant

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13
Q

What is the moles equation?

A

Moles = Mass / Mr

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14
Q

What is the limiting reactant?

A

It is the reactant that is used up in a reaction causing reaction to stop.

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15
Q

How do you find mass of product formed in reaction by limiting reactant?

A

1) Balance equation
2) Find out Mr of reactant and products we are focusing on
3) Find moles in limiting reactions (Moles = mass / Mr)
4) Use molar ratio to find moles in product
5) Find Mass (Mass = moles x Mr)

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16
Q

What is exothermic?

A

Exothermic gives out energy during a reaction and temperature increases.

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17
Q

What is endothermic?

A

Endothermic take in energy during a reaction and temperature decreases.

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18
Q

Energy profile diagram for exothermic?

A
  • X axis: progress of reaction
  • Y axis: Energy
  • The reactants are higher than the products
  • Activation energy line up
  • Energy released during reaction goes down
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19
Q

Energy profile diagram for endothermic?

A
  • Y axis: Energy
  • X axis: Progress of reaction
  • The reactants are lower than the products
  • Activation energy line up
  • Energy taken in during reaction line goes up
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20
Q

What is activation energy?

A

Activation energy is the energy required to start a chemical reaction.

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21
Q

What is bond breaking?

A

Bond breaking is when energy is absorbed to break bonds in reactants.
Bond breaking is endothermic

22
Q

What is bond making?

A

Bond making is when energy is released when new bonds are formed.
Bond making is exothermic

23
Q

What is the energy change equation?

A

Overall energy equation = energy required to break bonds - energy released to make bonds

24
Q

How do you know if a chemical reaction is exothermic or endothermic in terms of bond energies?

A

If overall energy is negative it is exothermic
-This means more energy is released in bond making than absorbed in bond breaking

If overall energy is positive it is endothermic.
-This means more energy is absorbed in bond breaking than released in bond making

25
Q

Acids:

A
  • Acids go from pH 1 - 6

- They contain H(+) Ions

26
Q

Alkali:

A
  • Alkali go from pH 8-14

- They contain OH(-) ions

27
Q

What do acid and alkali do when added to each other? + Equation

A

They neutralise each other

EQUATION FOR NEUTRALISATION
H(+) + OH(-) -> H20

28
Q

What is a strong acid?

A

Strong acids ionise completely in water and have low pH (acidic)

29
Q

What is a weak acid?

A

Weak acids partially ionise in water and tend to have higher acid pH (2-6)

30
Q

What is a concentrated and diluted acid?

A

Concentrated acids contain lots of H(+) Ions in a fixed volume

Dilute acids contain less H+ in that fixed volume

31
Q

What is concentration?

A

Refers to the number of ions in a fixed volume

32
Q

How does changing concentration affect pH

A
  • Increasing H(+) by factor of 10, decreases pH by 1 (more acidic)
33
Q

5 Acid reaction equations:

A

1) Acid + Metal oxide-> Salt + water
2) Acid + Metal hydroxide -> Salt + water
3) Acid + Alkali -> Salt + Water
4) Acid + Metal -> Salt + Hydrogen
5) Acid + Metal carbonate -> Salt + Water + Carbon dioxide

34
Q

What is a redox equation?

A

When oxidation and reduction occurs in a reaction.
Eg) Fe2O3 + 3CO -> 2Fe + 3CO2
Fe2O3 reduced to 2Fe
3CO oxidised to 3CO2

35
Q

What is oxidation?

A

Oxidation is the loss of electrons

Oxidation is the gain of oxygen

36
Q

What is reduction?

A

Reduction is the gain of electrons

Reduction is the loss of oxygen

37
Q

What is the oxidising agent?

A

It gets reduced (gains electrons or loses oxygen)

38
Q

What is the reducing agent?

A

It gets oxidised (loses electrons or gains oxygen).

39
Q

How do you make salts such as copper sulphate crystals?

A

Sulphuric acid + copper oxide -> Copper sulphate + water

1) Add reactants and stir making sure copper oxide is in excess
2) Filter off excess copper oxide
3) Leave filtrate to evaporate in dish and it will concentrate and crystallise

40
Q

What is the definition of electrolysis?

A

Electrolysis: The break down of molten or dissolved ionic compounds by electricity to form pure substance

41
Q

What are the electrodes and ions in electrolysis?

A

Cathode (-) attracts cations (+)

Anode (+) attracts anions (-)

42
Q

Electrolysis for molten compounds?

A
  • Positive ions (cations) attract cathode and gain electrons (reduced)
  • Negative ions (anions) attract to anode and lose electrons (oxidised)
43
Q

What happens at anode in electrolysis with dissolved compounds?

A
  • If halogen (F-,Cl-,Br-,I-) present halogen is produced.

- If Halogen not present (SO4,NO3,CO3) than oxygen is produced

44
Q

What happens at cathode in electrolysis with dissolved compounds?

A
  • If more reactive than hydrogen (K,Na,Ca,Mg,Zn,Fe,Pb) than hydrogen is produced
  • If less reactive than hydrogen (Cu,Ag, Au) than metal produced
45
Q

What the test for oxygen?

A

Glowing splint reignites

46
Q

What is the test for hydrogen?

A

Burning splint goes off with a squeaky pop

47
Q

What is the test for carbon dioxide?

A

When passed through limewater and makes it cloudy

48
Q

What is the test for Chlorine

A

Chlorine bleaches damp litmus paper

49
Q

Why are inert electrodes in electrolysis used?

A

They are used as they do not interfer with the reactions happening on the surface of the electrode as they are unreactive.

50
Q

How many particles, atoms, molecules or ions are there is one mole?

A

6.02 x 10^23

51
Q

What is an electrolyte?

A

The molten or dissolved ionic compound is an electrolyte.

52
Q

What is molar mass?

A

Mass in grams of 1 mole of a substance

CHEMISTRY (7 decks)

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