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Chemistry > DF 1-5 > Flashcards

DF 1-5 Flashcards

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1
Q

THE MOLE

A

A measure of the amount of particles in a substance (Avogadro’s constant = 6.02 x 10^23).

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2
Q

RELATOVE ATOMIC MASS

A

The mass of an element relative to carbon-12

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3
Q

RELATIVE FORMULA MASS

A

The mass of a compound relative to carbon-12

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4
Q

RELATIVE MOLECULAR MASS

A

The sum of all of the relative atomic masses of the atoms in a molecule

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5
Q

EMPIRICAL FORMULA

A

The simplest ratio of atoms in a compound

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6
Q

PERCENTAGE YEILD

A

Percentage yield is never 100%, this is because:

  • There are loss of products from reaction vessels - particularly if there are several stages to a reaction
  • Side reactions amy occur and produce unwanted by-products
  • Impurities in the reactions
  • Changes in temperature and pressure
  • If the reaction is an equilibrium system

The theoretical yield is the amount of product we expect to obtain from a reaction produced under ideal conditions

The experimental yield is the reduced amount of products

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7
Q

EPSOM SALTS

A

HYDRATED - Crystals contain water molecules
ANHYDROUS - Crystals which don’t contain water molecules
WATER OF CRYSTALISATION - Water molecules associated with ions in a crystal

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8
Q

EXOTHERMIC REACTION

A

A reaction that gives out energy and heats the surroundings. The products end up with less energy than the reactants had but the surroundings end up with more (heats the surroundings). The enthalpy change of exothermic reactions are always negative because energy is given out to the surroundings.

The energy needed to break the bonds is less than the energy needed to form the new bonds between the reactants so heat is give out to the surroundings

ENERGY IS RELEASED TO THE SURROUNDINGS BECAUSE MORE ENERGY IS RELEASED MAKING BONDS IN THE PRODUCTS THAN IS NEEDED TO BREAK THE BONDS IN THE REACTANTS.

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9
Q

ENDOTHERMIC REACTION

A

A reaction that takes in energy and cools the surroundings. In an endothermic reaction, the reactants take in energy from the surroundings leaving the products at a higher energy level than the reactants. The deltaH (enthalpy change) of endothermic reactions is always positive because energy is taken in from the surroundings.

In endothermic reaction the reactants take in energy from the surroundings, leaving the products at a higher energy level than the reactants, the enthalpy change of endothermic reactions is always positive excuse energy is taken in from the surroundings.

ENERGY IS TAKEN IN FROM THE SURROUNDINGS BECAUSE LESS HEAT ENERGY IS RELEASED MAKING BONDS IN THE PRODUCTS THAN IS NEEDED TO BREAK BONDS IN THE REACTANTS.

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10
Q

ENTHALPY CHANGE

A

The heat energy transferred in a reaction at a constant pressure

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11
Q

STANDARD CONDITONS ?

A

“WE HAVE SET STANDARD CONDITONS TO ALLOW US TO COMPARE ENTHALPY CHANGES”

  • TEMPERATURE - 298K (25 Degrees)
  • PRESSURE - 1 atm
  • CONCENTRATION - 1 mol dm^-3
  • STANDARD STATES - The physical state of a substance under standard conditions (liquid, solid or gas)
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12
Q

STANDARD ENTHALPY CHANGE OF A REACTION

A

The enthalpy change when molar quantities of reactants as stated in the equation react together under standard conditions

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13
Q

STANDARD ENTHALPY CHANGE OF COMBUSTION

A

The enthalpy change that occurs when one mole of a substance is burnt completely in oxygen under standard conditions in standard states. ALWAYS EXOTHERMIC

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14
Q

STANDARD ENTHALPY CHANGE OF FORMATION

A

The enthalpy change when one mole of a compound is formed from its elements under standard conditions in standard states.

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15
Q

STANDARD ENTHALPY CHANGE OF NEUTRALISATION

A

The enthalpy change when one mole of of hydrogen ions react with one mole of hydroxide ions to form one mole of water under standard conditions and in solutions containing 1 mol dm^-3.

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16
Q

Why are standard enthalpy changes of neutralisations often the same?

A

Because the same reaction is happening.

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17
Q

ENTHALPY CYCLES

A

Enthalpy cycles are used when its too difficult to calculate the enthalpy change directly. The enthalpy change for the indirect route is the same as the enthalpy change for the direct route, this is because energy cannot be created/destroyed (law of conservation of energy) so as long as your tarting and finishing points are the same - the enthalpy change will always be the same.

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18
Q

SPECIFIC HEAT CAPACITY

A

The specific heat capacity of a substance is the amount of energy needed to raise the temperature of 1g of a substance by 1K.

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19
Q

PRACTICE ENTHALPY CYCLES

A

PRACTICE ENTHALPY CYCLES

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20
Q

CRUDE OIL

A

Crude oil is a mixture of hydrocarbon compounds which can be separated by fractional distillation.

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21
Q

FRACTIONAL DISTILATION

A
  • Crude oil is heated to vaporise it and then the vapours pass into a fractioning column
  • The oil is separated into fractions each having a specific boiling point range - they don’t have exact boiling points because they’re a mixture of many different hydrocarbons.
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22
Q

CARBON (CRUDE OIL)

A

Carbon forms strong covalent bonds with its self to give chains and rings of its atoms joined by carbon-carbon covalent bonds. This property is called catenation and leads to the limitless variety of organic compounds possible. EACH CARBON ATOM CAN FORM FOUR COVALENT BONDS AND THE CHAINS MAY BE STRAIGHT OR BRANCHED.

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23
Q

HYDROCARBONS

A

Compounds containing only carbon and hydrogen atoms

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24
Q

AROMATIC COMPOUNDS (SUCH AS ARENES)

A

Compounds that contain one or more benzene rings

25
Q

ALIPHATIC COMPOUNDS

A

Compounds that don’t contain any benzene rings

26
Q

SATURATED

A

Hydrocarbons that contain the maximum number of hydrogen atoms possible, no carbon-carbon double or triple bonds.

27
Q

HOMOLOGOUS SERIES

A

A series of compounds in which all members have the same general molecular formula.

28
Q

FUNCTIONAL GROUP

A

Modifiers that are responsible for the characteristic chemical reactions of molecules.

29
Q

ALKANES (ALIPHATIC COMPOUND)

[CnH2n+2]

A

Alkanes are saturated because every carbon atom in an alkane has four single bonds with other atoms and its impossible for carbon to make more than four bonds, so alkanes are saturated.

Alaknes can be represented in a skeletal formula where functional groups attached are called alkyls (Methyl, ethyl, propyl, butyl etc).

Alkane molecules with cyclic structures also exist - they have a ring of carbon atoms, with 2 hydrogen atoms attached to each carbon atom (4 bonds = saturated).

30
Q

STRUCTURAL ISOMERS

A

Structures that have the same molecular formula but different structural formula.

31
Q

ALKENES (ALIPHATIC COMPOUNDS)

[CnH2n]

A

Alkenes are hydrocarbons because they’re only made up of hydrogen and carbon atoms.

Alaknes are UNSATURATED because they contain at least one carbon-carbon covalent bond (double bond or triple bond) which means that they can bond to extra atoms in ADDITION REACTIONS.

32
Q

BENZENE (ARENES/AROMATIC COMPOUNDS)

A

Benzene is a cyclic alkene with 6 carbon atoms and 3 double bonds - its relatively stable though because the double bond electrons are delocalised around the carbon ring (can flow around freely) and this is why the symbol can have a circle in it

33
Q

REPRESENTING ORGANIC COMPOUNDS

A
  • GENRAL FORMULA - A formula that can describe any member of a family of compounds
  • MOLECULAR FORMULA - The actual number of atoms of each element in a molecule
  • SHORTENED STRUCTURAL FORMULA - Shows the atoms, carbon by carbon with the attached hydrogens and functional groups
  • STRUCTURAL FORMULA - Shows how all of the atoms are arranged and all the bonds between them
  • SKELETAL FORMULA - Shows the bonds of the carbon skeleton only, with any functional groups.
34
Q

ENERGY DENSITY

A

How much energy you obtain per kilogram of fuel

35
Q

BOND ENTHALPIES

A

A chemical bond is an electrical attraction between atoms or ions - breaking a bond involves overcoming these attractive force. To break the bond completely, the atoms/ions need to be a infinite distance apart

THE QUANTITY OF ENERGY NEEDED TO BREAK A BOND

BOND ENTHALPIES INDICATE HOW STRONG A BOND IS - THE STRONGER THE BOND THE MORE ENERG IS NEEDED TO BREAK IT AND THEREFORE THE HIGHER THE BOND ENTHALPY.

36
Q

BOND ENTHALPY AND BOND LENGTH

A
  • When a bond forms, the atoms move together because of the attractive forces between the nuclei and electrons - also repulsive forces between the nuclei of the two atoms.
  • These forces get larger as the atoms approach until the atom stop moving together. The distance between them is called the equilibrium bond length. The shorter the bond length - the stronger the attraction between the atoms
37
Q

Why is it difficult to measure bond enthalpies?

A

Difficult to measure bond enthalpies because theres often more than one type of bond in a compound - also difficult to make measurements when everything is in the gaseous state. For this reason bond enthalpies are measured indirectly using enthalpy cycles.

38
Q

BREAKING AND MAKING BONDS IN A CHEMICAL REACTION

A

BOND BREAKING - Endothermic, so bond enthalpies are always positive
BOND MAKING - Exothermic

  • You need to break bonds before product molecules can begin to form, many reactions need to be heated to break the bonds.
  • ALL REACTIONS INITIALLY NEED ENERGY TO STRETCH AND BREAK BONDS
  • Some reactions only need a small amount of energy and there’s enough in the surroundings at room temperature
  • It isn’t necessary for all bonds to be broken before a reaction gets going, once bonds have broken, new bonds can start to form and this usually gives out enough energy to keep the reaction going.
39
Q

AVERAGE BOND ENTHALPY

A

The average quantity of energy required to break a particular bond

40
Q

BOND ENTHALPIES (DEFINITION)

A

The energy needed to break one mole of a bond to give separate atoms all in a gaseous state - Always positive because bond breaking is endothermic.

41
Q

BREAKING BONDS

A

Breaking bonds involves using energy to overcome the forces of attraction

42
Q

BOND ENTHALPY TRENDS

A
  • DOUBLE BONDS HAVE MUCH HIGHER BOND ENTHALPIES THAN SINGLE BONDS, TRIPLE BOND ENTHALPIES ARE EVEN HIGHER
  • THE HIGHER THE BOND ENTHALPY - THE SHORTER THE BOND, THIS IS BECAUSE THERE ARE MORE ELECTRONS BETWEEN THE ATOMS BEING ATTRACTED TO THE POSITIVE NUCLEI, THE MORE ATTRACTION MAKES SHORTER BONDS.
43
Q

THEORETICAL CALCULATIONS

A

Theoretical calculations are different to experimental results, this is because;

  • They’re often averages from several compounds
  • The experiment uses the element in a different state to the standard conditions
44
Q

CATALYSIS

A

The process of speeding up a chemical reaction using a catalyst

45
Q

HOMOGENOUS CATALYSIS

A

If the catalyst and reactants are in the same physical state then the reaction is HOMOGENOUS CATALYSIS. For example enzyme-catalysed reactions in cells take place in aqueous solution and are examples of this type of catalysis.

46
Q

HETEROGENEOUS CATALYSIS (DEFINITION)

A

Where the catalyst and the reactants are in different physical states.
Usually the catalyst is solid and the reactants are liquids or gases

47
Q

HETEROGENOUS CATALYSIS

A

When a solid catalyst is used to increase the rate of reaction between gases or liquids - the reaction occurs on the surface of the solid. The reactants from bonds with the atoms on the surface of the catalyst and they’re ADSORBED ONTO THE SURFACE. As a result, bonds in the reactant molecules are weakened and break and new bonds from between the reactants. This weakens the bonds to the catalyst surface and the product molecules are released (the product diffuses away).

48
Q

CATALYST POISONING (DEFINITION)

A

A substance that stops a catalyst functioning properly

49
Q

CATALYST POISONING

A

In heterogenous catalysis, the poison molecules are adsorbed more strongly onto the catalyst surface than the reactant molecules - the catalyst cannot catalyse a reaction of the poison and so becomes inactive, with poison molecules blocking the active sites on its surface.

50
Q

CLEANING A CATALYST

A

Sometimes catalysts can be cleaned/their surface is regenerated. for example in the cracking of a long chained hydrocarbon, carbon is produced and the surface of the catalyst becomes coated in a layer of soot. This blocks the adsorption of reactant molecules and the activity of the catalyst is reduced. The catalyst is constantly recycled through a separate container where hot air is blow through the powder, the oxygen in the air converts the carbon (soot) to carbon dioxide and cleans the catalyst surface.

51
Q

What is a catalyst?

A

A catalyst is a substance that increases the rate of reaction by providing an alternative reaction pathway with a lower activation energy, catalysts aren’t used up in reactions and can be recovered chemically unchanged at the end.

52
Q

What are many heterogenous catalysts?

A

TRANSITION METALS

53
Q

Catalysts in cracking

A

Catalysts can be used to crack long chained hydrocarbons into smaller chained hydrocarbons - however there is no guarantee on the size of the new chain because the products of cracking are random. Catalysts are used to crack long chained hydrocarbons into small chained hydrocarbons because they are more useful.

54
Q

Why are catalysts used in cracking?

A

Without a catalyst, cracking requires extremely high temperatures and pressures - this is very costly. Catalysts reduce the cost of cracking.

55
Q

How are catalysts used in cracking?

A

hydrocarbon vapours are passed over a heated catalyst - this saves a lot of money because lower temperatures of around 450 degrees and low pressures are suitable for the reaction to occur.

56
Q

what catalyst is used in the hater process to make ammonia (NH3) ?

A

Iron

57
Q

What catalyst is used in catalytic converters?

A

Platinum

58
Q

whats the term for when new molecules detach from the catalyst surface in heterogenous catalysis?

A

DESORPTION

Chemistry (11 decks)

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