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CHEMISTRY > Stoichiometric Relationship > Flashcards

Stoichiometric Relationship Flashcards

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1
Q

Matter can exist in different states of matter depending on?

A

The temperature and pressure

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2
Q

what is dependent on the amount of kinetic energy that the particles possess?

A

the different arrangement and movement of the particles.

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3
Q

What is kinetic energy

A

the energy related to the motion (or movement) of an object

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4
Q

What are Changes of state at constant pressure directly related to ?

A

changes in temperature.

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5
Q

What causes changes in states of matter?

A
  • When heated, the particles of a substance gain kinetic energy
  • They are able to overcome the intermolecular forces that exist between them
  • This results in a change of state
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6
Q

What is sublimation and what happens to heat for it to happen?

A
  • Solid to gas
  • Heat is absorbed
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7
Q

What is deposition and what happens to heat for it to happen?

A

-Gas to solid
- heat is released

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8
Q

What is evaporation and what happens to heat for it to happen?

A

-liquid to gas
- heat is absorbed

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9
Q

What is boiling and what happens to heat for it to happen?

A
  • liquid to gas
  • Heat is absorbed
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10
Q

What is condensation and what happens to heat for it to happen?

A
  • Gas to liquid
  • Heat is released
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11
Q

What is freezing and what happens to heat for it to happen?

A
  • Liquid to solid
  • heat is released
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12
Q

What is melting and what happens to heat for it to happen?

A
  • Solid to liquid
  • Heat is absorbed
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13
Q

Provide examples of substances that undergo sublimation at atmospheric pressure (3)

A
  • Iodine
  • Carbon Dioxide
  • Ammonium Chloride
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14
Q

How does evaporation differ from boiling?

A
  • Evaporation differs from boiling in that it takes place only at the surface of a liquid and can occur at temperatures below the boiling point of the liquid
  • Boiling occurs at a specific temperature and takes place throughout the liquid. Bubbles of gas are formed within the liquid, not only at the surface.
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15
Q

How can changes in state be represented in equations? (3)

A
  • Melting: H2O (s) → H2O (l)
  • Sublimation: I2 (s) → I2 (g)
  • Condensation: H2O (g) → H2O (l)
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16
Q

Why is it that during a change in state the temperature remains constant?

A

At these points, the energy is being used to overcome the intermolecular forces that exist between the particles.

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17
Q

What is the density of water in g/cm^{3}

A

1.00 g/cm^{3}

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18
Q

What is an atom?

A

It is the smallest particle that shows the characteristic properties of that element

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19
Q

What is an element?

A

is made up of the same kind of atom and cannot be broken down by chemical means into a simpler substance.

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20
Q

How many element on the periodic table occur naturally

A

92 Elements

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21
Q

What are metalloids

A

These are elements that have properties of both metals and non-metals

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22
Q

What is a compound?

A

it is made up of two or more different elements that are chemically combined.

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23
Q

Provide examples of compounds that exist as discrete molecules?

A
  • Water (H2O)
  • Ethanol ( C2H5OH)
  • Carbon Dioxide (CO2)
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24
Q

What is a molecule?

A

It consists of two or more atoms that are chemically bonded together. The atoms can be the same, as in O2, or different, as in H2O.

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25
Q

Why are molecules such as H2, O2, N2 not compounds?

A

It is because they are composed of the same kind of atom bonded together.

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26
Q

What is a mixture?

A

It is composed of two or more substances that are not chemically combined, meaning that each substance retains its original properties.

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27
Q

What is a homogeneous mixture?

A

A homogeneous mixture has the same composition throughout

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28
Q

What is a heterogeneous mixture?

A

A heterogeneous mixture has a non-uniform composition.

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29
Q

How can homogeneous mixtures be separated?

A

Through fractional distillation which is base on the principle that elements have different boiling points

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30
Q

What is fractional distillation?

A

This is a is a technique that is used to separate the components of a mixture based on their different boiling points.

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31
Q

What is concentration?

A

This is the amount of solute dissolved in a known volume of a solution

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32
Q

Why is the resultant volume of the mixture of ethanol and water less than the individual volumes?

A

This is caused by the close packing of the ethanol and water molecules when they are mixed together.

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33
Q

What do we call liquids that cannot mix together

A

immiscible i.e Oil and Water

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34
Q

Why can heterogeneous mixtures be separated by physical means?

A

This is because they form layers when mixed together, they don’t form a uniform mixture

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35
Q

What does the law of conservation of mass state?

A

mass is conserved in a chemical reaction

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36
Q

What are stoichiometric coefficients and do they do?

A
  • These are the numbers in front of each formula in a balanced equation
  • They tell us the molar ratios of the reactants and products in a balanced equation
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37
Q

What types of reactions allow the use of stoichiometric coefficients as fractions?

A

In combustion reactions

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38
Q

Define a precipitate and identify it in a chemical reaction between aqueous silver nitrate, AgNO3, and aqueous sodium chloride, NaCl

A
  • Precipitate is an insoluble solid that forms out of a solution
  • AgNO3 (aq) + NaCl (aq) → AgCl (s) + NaNO3 (aq)
  • AgCl (s), is the precipitate
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39
Q

Provide examples of elements that exist as diatomic molecules under standard conditions

A

hydrogen (H2)
oxygen (O2)
nitrogen (N2)
fluorine (F2)
chlorine (Cl2)
bromine ( Br2)
iodine ( I2)

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40
Q

what is relative atomic mass?

A

This is the weighted average mass of an atom compared to 1/12 the mass of an atom of carbon-12.

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41
Q

What is an atomic mass unit?

A

The mass of 1/12 of an atom of carbon-12

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42
Q

Why is carbon-12 used as a reference?

A

It is because its mass can be accurately measured and it is the most abundant stable isotope of carbon.

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43
Q

What is the relative formula (or molecular) mass (Mr) of a compound

A

This is the weighted average mass of the compound compared to 1/12 the mass of an atom of carbon-12.

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44
Q

What is the difference between relative formula (RFM) mass and relative molecular mass (RMM) ?

A

RFM is used with Ionic compounds such as NaCl and RMM is used with covalent compounds such as O2, CO2, H2O

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45
Q

What is amount of substance (n)?

A

The amount of substance is a measure of the number of specified elementary entities in a sample

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46
Q

What elementary particles are referred to by amount of substance?

A

Elementary entities can refer to atoms, molecules, ions, electrons or any other particle.

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47
Q

What is the Avogadro constant?

A
  • (symbol L or NA) is a proportionality factor that relates the amount of substance with the number of particles.
  • 6.02 X 10^{23} mol^{-1}
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48
Q

What is the difference between the Avogadro constant and the Avogadro number?

A

The Avogadro number is dimensionless

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49
Q

What is molar mass?

A

This is the mass in grams of one mole of a substance. The unit for molar mass is grams per mole (g mol-1)

50
Q

What is the difference between molar mass and relative atomic mass?

A

Relative molecular mass is dimensionless with molar mass having a unit of g mol^{-1}

51
Q

What is the relationship between moles, mass and molar mass?

A

n (mol) = (mass (g) )/ (Molar mass (g mol−1))

52
Q

How is the mass of one molecule of a substance calculated?

A

Mass of one molecule = (molar mass of substance) / (Avogadro constant)

53
Q

What is the empirical formula?

A

This is the lowest whole number ratio of atoms (or ions) in a compound.

54
Q

What is the molecular formula?

A

This is the actual number of atoms in a compound.

55
Q

What is percentage composition by mass?

A

It expresses the mass of each element in a compound as a percentage

56
Q

How do you calculate the percentage by mass of an element in a compound?

A

Percentage composition=|(mass of element in compound) / (molar mass of compound) |×100%

57
Q

What possible errors are present when doing the combustion of magnesium experiment for determining Empirical formula of magnesium-oxide? (3)

A
  • The magnesium used was not pure
  • The product was something other than magnesium oxide (such as magnesium nitride, Mg3N2)
  • Some product was lost when the lid was removed to allow oxygen in
58
Q

In an experiment to calculate water of crystallization, what are the assumptions made with this method?

A
  • The mass change is only due to the water lost from the hydrated salt
  • The crucible does not absorb water
  • The anhydrous salt does not decompose
59
Q

How to determine the molecular formula of a compound given the Empirical formula?

A
  • Find the molar mass of the compound
  • Find the molar mass of the empirical formula
  • Molar mass of compound / molar mass of the empirical formula, gives a scalar
  • Multiply this by the empirical formula to get molecular formula
60
Q

What was stated in Dalton’s atomic theory?

A
  • Atoms are tiny particles made of elements
  • Atoms cannot be divided
  • All the atoms in an element are the same
  • Atoms of one element are different to those of other elements
61
Q

What did Thompson discover about electrons? (3)

A
  • They have negative charge
  • They can be deflected by electromagnetic fields
  • They have very small mass
62
Q

Explain the current model of the atom

A
  • Protons and neutrons are found in the nucleus
  • Electrons orbit the nucleus in shells
  • The nucleus is tiny compared to the total volume of atom
  • Most of atom’s mass is in the nucleus
  • Most of the atom is empty space between the nucleus and the electrons
63
Q

What is the charge of a proton and an electron?

A

proton = +1
Electron = -1

64
Q
A
65
Q

Which two particles make up most of an atom’s mass?

A

Protons and neutrons

66
Q

What does the atomic number show about an element?

A

Atomic number = number of protons in an atom

67
Q
A
68
Q

How to calculate the number of neutrons?

A

Number of neutrons = mass number - atomic number

69
Q

Define the term isotope

A

Atoms of the same element with different number of neutrons and therefore different mass number

70
Q

Why do different isotopes of the same element react in the same way? (2)

A
  • Neutrons have no impact on the chemical reactivity
  • Reactions involve electrons, isotopes have the same number of electrons in the same arrangement
71
Q

define relative atomic mass

A

The weighted mean mass of an atom of an element compared with one twelfth of the mass of an atom of carbon -12

72
Q

Define relative isotopic mass

A

The mass of an atom of an isotope compared with one twelfth of the mass of an atom of the carbon-12

73
Q

The relative isotopic mass is same as which number ?

A

mass number

74
Q

what two assumptions are made when calculating mass number?

A
  1. Contribution of the electron is neglected
  2. Mass of both proton and neutron is taken as 1.0 u
75
Q

How to calculate the relative molecular mass and relative formula mass?

A

Both can be calculated by adding the relative atomic masses of each of the atom making up the molecule of the formula

76
Q

What are the uses of mass spectrometry? (3)

A
  • identify unknown compounds
  • Find relative abundance of each isotope of an element
  • Determine structural information
77
Q

What does the principal quantum number indicate?

A

The shell occupied by the electrons

78
Q

What is a shell?

A

A group of orbitals with the same principal quantum number

79
Q

How many electrons can the 1st shell hold?

A

2

80
Q

How many electrons can the 2nd shell hold?

A

8

81
Q

How many electrons can the 3rd shell hold?

A

18

82
Q

How many electrons can the 4th shell hold?

A

32

83
Q

What is an orbital?

A

A region around the nucleus that can hold up to two electrons with opposite spins

84
Q

How many electrons can an orbital hold?

A

2

85
Q

What are the 4 types of orbitals?

A
  • s orbital
  • p orbital
  • d orbital
  • f orbital
86
Q

what is the shape of an s orbital?

A

Spherical

87
Q

What is the shape of a p-orbital?

A

Dumb-bell shape

88
Q

How many orbitals are found in an S- subshell?

A

1

89
Q

How many electrons can be held in an S-subshell

A

2

90
Q

How many orbitals does a p- subshell have?

A

3

91
Q

How many electrons can be held in a p-subshell?

A

6

92
Q

How many orbitals are present in a D-subshell?

A

5

93
Q

How many electrons can be held in a d-subshell?

A

10

94
Q

How many orbitals are found in an F-subshell?

A

7

95
Q

How many electrons can fill an F-subshell?

A

14

96
Q

When using ‘electrons in box’ representation, what shape is used to represent the electrons?

A

Arrows

97
Q

What letter is used to represent shell number?

A

n

98
Q

From which shell onwards is S-orbital present?

A

n=1

99
Q

From which shell onwards is p-orbital present?

A

n = 2

100
Q

From which shell onwards is d-orbital present?

A

n=3

101
Q

From which shell onwards is F-orbital present?

A

n= 4

102
Q

What are the rules by which electrons are arranged in the shell? (5)

A
  • Electrons are added one at a time
  • Lowest available energy level is filled first
  • Each energy level must be filled before the next one can fill
  • Each orbital is filled singly before pairing
    -4s is filled before 3d
103
Q

Why does 4s orbital fill before 3d orbital?

A

4s orbital has a lower energy than 3d before it is filled

104
Q

What is the electron configuration of krypton?

A

1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6

105
Q

How can electron configuration be written in short?

A
  • The noble gas before the element is used to abbreviate
  • E.g. Li –> 1s2 2s1; Li–> [He] 2s1
106
Q

How are the elements arranged in a periodic table?

A

Group number = number of electrons in the outer shell

107
Q

What is a period on a periodic table?

A

The horizontal rows

108
Q

What is a group on a periodic table?

A

The vertical columns

109
Q

How is the group number related to the number of electrons?

A

They are arranged in the order of increasing atomic numbers

110
Q

Does the group number indicate horizontal or vertical columns in the periodic table?

A

vertical column

111
Q

What is meant by periodicity?

A

The repeating trends in the chemical and physical properties

112
Q

What change happens across each period?

A

Elements change from metals to non-metals

113
Q

Define first ionization energy

A

The energy required to remove a mole of electrons from a mole of gaseous atoms to form one mole of gaseous 1+ ions under standard conditions

114
Q

Write an equation for the first ionization energy of magnesium

A

Mg (g) –> Mg+ (g) + e-

115
Q

What are the factors that affect ionization energy?

A
  • Atomic radius
  • Nuclear charge
  • Electron shielding or screening
116
Q

Why does first ionization energy decrease between group 2 and 3?

A
  • Decreases between 2 and 3 because in period 3 the outermost electrons are in p-orbitals
  • Whereas in group 2 are in s-orbital, so the electrons are easier to be removed
117
Q

Why does first ionization energy decrease between group 5 and 6?

A
  • The decrease between 5 and 6 is due to the group 5 electrons in p-orbitals which are single electrons
  • In group 6 the outermost electrons are spin paired, with some repulsion
    -Therefore the eletrons are slightly easier to remove
118
Q

Does first ionization increase or decrease between the end of one period and the start of next? Why?

A
  • Decrease
  • There is increase in atomic radius
  • increase in electron shielding
119
Q

Does first ionization increase or decrease down a group? why?

A
  • Decrease
  • Shielding increases –> weaker attraction
  • Atomic radius increases –> distance between the outer electrons and nucleus increases–> weaker attraction
  • increase in number of protons is outweighed by increase in distance and shielding
120
Q

Describe the structure, forces and boding in every element across period 2

A
  • Li and Be –> giant metallic; strong attraction between positive ions and delocalized electrons; metallic bonding
  • B and C –> Giant covalent; strong forces between atoms; covalent
  • N2, O2, F2, Ne –> Simple molecular; Weak intermolecular forces between molecules; covalent bonding within molecules and intermolecular forces between molecules
121
Q

Describe the structure, forces and bonding in every element across period 3

A
  • Na, Mg, Al –> Giant metallic; strong attraction between positive ions and delocalized electrons; metallic bonding
    -Si –> Giant covalent; strong forces between atoms; covalent
  • P4, S8, Cl2, Ar –> Simple molecular; Weak intermolecular forces between molecules; covalent bonding within molecules and intermolecular forces between molecules

CHEMISTRY (11 decks)

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