AQA A LEVEL CHEMISTRY Samenvattingen, Aantekeningen en Examens

What is enthalpy change? Heat energy transferred in a reaction at constant pressure What are standard conditions for enthalpy change? 100kPa and stated temperature (normally 25 degrees celcius) What values of deltaH do exothermic reactions have? Negative (less than 0) What values of deltaH do endothermic reactions have? Positive (more than 0) What do exothermic reactions do with energy? Give out energy What do endothermic reactions do with energy? Absorb energy Are oxidation reactions endo...

Proton Mass 1 Proton Charge +1 Neutron Mass 1 Neutron Charge 0 Electron Mass 1/1840 Electron Charge -1 Atomic Number number of protons in the nucleus of an atom Mass Number number of protons and neutrons in the nucleus of an atom Isotopes atoms of the same element with a different number of neutrons Why do isotopes have the same chemical properties? Same number of outer shell electrons TOF Mass Spec... 4 key stages? Ionisation Acceleration Separation of ions Detection Electron impact ...

Explain why CF4 has a bond angle of 109.5°. -there are 4 bonding pairs and no lone pairs -repel equally and therefore spread apart as far as possible Topic 4 Energetics State and explain change in the volume of water in calorimetry that would cause a reduction in heat loss. -higher volume -smaller increase in temperature above room temperature / increased contact with calorimetry / smaller heat loss by evaporation Define the term standard enthalpy of combustion. The enthalpy change when one ...

What are nucleons? Nucleons are protons and neutrons in the nucleus. What is the position of protons? Nucleus What is the relative mass of a proton 1 What is the relative charge of a proton? +1 What is the position of neutrons? Nucleus What is the relative mass of a neutron? 1 What is the relative charge of a neutron? 0 What is the position of electrons? Orbitals What is the relative mass of an electron? 1/1800 What is the relative charge of an electron? -1 Define mass number Sum of pr...

What is heterolytic fission? Where one ion gets both electrons from the covalent bond What are produced by heterolytic fission? Ions What is a free radical? An atom or group with an unpaired electron, which is highly reactive as it wishes to pair up this electron What are 3 examples of situations where a free radical can be formed? During thermal cracking, during the reaction of halogens and methane, by homolytic fission What is homolytic fission? A reaction where each atom gets one electron...

What is an alkene? An unsaturated hydrocarbon What is an unsaturated hydrocarbon? A compound containing only carbon and hydrogen atoms and containing at least one carbon carbon double bond What are van der Waals forces? Relatively weak intermolecular forces caused by temporary dipole dipole interaction What is the general formula for an alkene? CnH2n How would you name an alkene given its displayed formula? Identify the longest carbon chain Identify the position of the carbon carbon double b...

Relative atomic mass The average mass of an atom of an element, relative to 1/12th of the mass of an atom of Carbon-12 Relative molecular mass Average mass of a molecule compared to 1/12th of the mass of a carbon-12 atom The Avogradro constant the number of particles in a mole ideal gas equation pV = nRT empirical formula the simplest whole number ratio of atoms of each element in a compound percentage atom economy (Mass of desired product/total mass of reactants) x 100 ionic bonding the e...

TOF steps 1) ionisation 2) acceleration 3) ion drift 4) detection 5) analysis Electron impact Sample vaporised and electron gun fires high energy electrons at it which knock off 1 electron from each particle, making them 1+ ions NB- can knock off more than one e or break molecular ion electrospray ionization Sample dissolved in volatile solvent then injected through needle to give fine mist which is attached to positive end of high voltage power supply, particles gain proton NB- Mr of substanc...

Periodic table Table that provides chemists with a structural organisation of the known chemical elements that can be used to deduce physical and chemical properties Atomic radius across Period 3 Decreases First ionisation energy across Period 3 Increases Exceptions: Drops at Al and S Melting points across Period 3 Increases from Na to Si Decreases from Si to Ar Small rise at S Explain why the melting point of aluminium is higher than the melting point of sodium Bigger charge (3+ compared to...

What are standard conditions? 298K/25°C 100kPa/1 atm 1 moldm-3 Enthalpy change of formation The enthalpy change when 1 mole of a compound is formed from its constituent elements under standard conditions, with all reactants and products in their standard states. Enthalpy change of combustion The enthalpy change when 1 mole of a substance is burned completely in oxygen. Enthalpy change of atomisation The enthalpy change that accompanies the formation of 1 mole of gaseous atoms from the elemen...