A Level Chemistry

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Which letter is used to represent the atomic number of an atom
z
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What does the atomic number tell us about an element?
Atomic number = number of protons in an atom
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What letter represents mass number?
A
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How is the mass number calculated
mass number = number of protons + number of neutrons (total number of nucleons)
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Define relative atomic mass
Average mass of all isotopes of an element compared to ¹/₁₂ the mass of an atom of Carbon 12 (C¹²)
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What is are isotopes of an element?
Different forms of the same element, containing the same number of protons but different numbers of neutrons. They still have the same chemical propertie
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How many orbitals and electrons do these shells contain? a) 1s b) 2p c) 3s d) 3d d) 4s
a) 1s- 1 orbital, 2 electrons b) 2p- 3 orbitals, 6 electrons c) 3s- 1 orbital, 2 electrons d) 3d- 5 orbitals, 10 electrons e) 4s- 1 orbital, 2 electrons
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Does 3d or 4s have a higher energy?
3d
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What is an orbital?
A region around the nucleus that can hold up to two electrons
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What would be the relationship between 2 electrons in the same orbital in terms of their spin?
Have opposite spin as repel each other as both negative
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Explain why chromium does not fit the trend for electronic configuration
It only has one electron in its 4s orbital before filling 3d 1s² … 3p⁶ 4s¹ 3d⁵
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Explain why copper does not for the trend for electronic configuration
It only has one electron in its 4s orbital before filling 3d 1s² … 3p⁶ 4s¹ 3d¹
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What are the two types of ionisation for a mass spectrometer? How do they differ
1. Electron impact: electron gun (hot wire filament with current through it emitting electrons) knocks off one electron from each particle to form 1+ MOLECULAR IONS (these ions fragment). 2. Electrospray: sample dissolved in volatile solvent (e.g. wa
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When would you use the different types of ionisation in a mass spec?
Electron impact used for organic or inorganic molecules with a low formula mass. Electrospray used for substances with a higher molecular mass including biological molecules, e.g. proteins
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Describe how a time of flight mass spectrometer works
Acceleration - positive ions attracted towards a negatively charged plate. Ion Drift - ions pass through hole in plate, form a beam with constant kinetic energy, travel along tube to detector. Time of flight is therefore directly proportional to the
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Define first ionisation energy
The energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous 1+ ions
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What energy change is breaking bonds associated with?
Energy is taken in to break bonds → endothermic reaction
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What energy change is making bonds associated with?
Energy is released to make bonds → exothermic reaction
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What are some uses of thermochemistry?
Measuring and comparing the energy values of fuels Calculating the energy requirements for industrial processes Working out the theoretical amount of energy released/taken in in a reaction Predicting if a reaction will take place or not
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What is an endothermic reaction?
One with an overall positive enthalpy change (+ΔH) → energy in breaking bonds > energy out making bonds
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What is an exothermic reaction?
One with an overall negative enthalpy change (-ΔH) → energy in breaking bonds < energy out making bonds
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If a reversible reaction is endothermic one way, what type of the reaction is the other way?
exothermic
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Give 2 examples of exothermic reactions
Combustion of fuels Neutralisation
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Give an example of an endothermic reaction
Thermal decomposition
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Define enthalpy change; what symbol is used to represent it?
Energy change of a system at a constant pressure represented by ΔH
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What are the standard conditions?
100kPa / 1atm pressure 298K / 250C temperature
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What does “in standard state” mean?
The state an element/compound exists at in standard conditions (100kPa, 298K)
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Define standard enthalpy of formation
The enthalpy change when one mole of a compound is formed from it constituent elements in standard conditions (100kPa, 298K), with reactants and products in their standard states.
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Give an example of an equation which represents standard enthalpy of formation
There are many e.g. H2 (g) + ½ O2 (g) → H2O (l)
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Define standard enthalpy of combustion
The enthalpy change when one mole of a substance is burnt completely in oxygen in standard conditions (100kPa, 298K), with reactants and products in their standard states.
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Give an example of an equation which represents standard enthalpy of combustion
E.g. C (s) + O2 (g) → CO2 (g)
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What is the difference between heat and temperature?
Heat is the sum of all particles’ energy, therefore it is affected by the amount of substance; temperature is related to the mean kinetic energy of the particles in a system, so is independent of the number of particles present.
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How can you calculate enthalpy change from experimental data?
Use the equation Q = mcΔT, where m is the mass of the substance being heated (usually water), c is the specific heat capacity of that substance (water’s SHC = 4.18gJ-1K-1) and ΔT is the change in temperature
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How could this calorimeter be made more accurate?
Add draught screens at the sides, add a lid on top of the beaker, add mineral wool around the beaker → all to insulate and reduce heat lost to the surroundings
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What is a flame calorimeter; how does it differ to a simple calorimeter?
Reduces heat lost to the surrounding to give more accurate results: has a spiral chimney made of copper, an enclosed flame and the fuel is burnt in pure oxygen, not air.
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How would you measure the enthalpy change for a reaction occurring in (aq)?
Use an expanded polystyrene cup as a calorimeter (good insulator → reduce heat loss). Heat is generated in the solution; measure this temperature change. Take heat capacity of solution to be 4.18 and density of solution = 1gcm-3.
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What can you use to make experimental determination of enthalpy change of reaction more accurate?
What can you use to make experimental determination of enthalpy change of reaction more accurate?
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What is Hess’s Law?
States that the enthalpy change for a reaction is the same regardless of the route taken
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What is the enthalpy of an element?
The enthalpy of all elements in their standard states (the states in which they exist at 100kPa and 298K) is defined as 0
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Define bond dissociation enthalpy.
The enthalpy change required to break a covalent bond, with all species in the gaseous state; differs for the same bond type in different molecules.
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Define mean bond enthalpy.
Average value (across different chemical environments) for the bond dissociation enthalpy of a given bond.
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Why may experimental methods for enthalpy determination not be very accurate?
Heat is lost to the surroundings Not in standard conditions Reaction may not go to completion
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Why will using bond enthalpies not be as accurate as using standard enthalpy of combustion/formation?
Bond enthalpies are a mean for the same bond across different molecules; standard enthalpy of combustion and formation apply just to that molecule, therefore they are more accurate
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Other cards in this set

Card 2

Front

What does the atomic number tell us about an element?

Back

Atomic number = number of protons in an atom

Card 3

Front

What letter represents mass number?

Back

Preview of the front of card 3

Card 4

Front

How is the mass number calculated

Back

Preview of the front of card 4

Card 5

Front

Define relative atomic mass

Back

Preview of the front of card 5
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