chemistry spring revision 2025

• how to calculate the Ar value of isotopes

  (% x amount) + (% x amount) /100
• methane

  CH4
• ethene

  C2H4
• ethane

  C2H6
• Ammonia

  NH3
• hydrogen chloride

  HCl
• number of shells shows.....

  period number on periodic table
• number of electrons on outer shell shows.....

  group number on periodic table
• define isotopes

  atomes of the same element with the same proton number but different neutron number
• what are the charges of each sub-atomic particle

  electron= - proton= + neutron=0
• PH of metals

  above PH7 - alkali
• PH of non-metals

  below PH 7 -acidic
• why do the elements in the same group have similar properities

  because they have the same number of electrons on the outer shell
• why are noble gases unreactive/inert

  because they have a full outer shell
• what colour and state is chlorine, brominr and iodine at room temp

  chlorine- poisonous green gas

  bromine-poisonous brow liquid

  iodine-grey solid
• as you go down group 7 the reactivity.....

  decreases- more shells means further away from nucleus and so harder to gain an electron to become an ion
• displacemt reaction table


  below:

  
• balanced equation of chlorine reaction with potassium bromide

  Cl2 +2KBr - Br2 +2KCl
• balanced equation of chlorine reaction with potassium iodide

  Cl2 +2KI - I2 + 2KCl
• balanced equation of bromine reaction with potassium iodide

  Br2 + 2KI - I2 + 2KBr
• oxygen

  O2
• carbon dioxide

  CO2
• why do simple molecular substances have low melting and boiling point at room temp

  because although the atoms have strong covalent bonds, they have weak intermolecular forces holding the molecules together this means it takes little energy to seperate them and therefore a low mp and bp.
• As relative molecular mass increases, intermolecular forces....

  get stronger because there are more points along the bigger molecule for the intermolecular forces to work on and so more energy will be needed to break the molecules up so a higher mp and bp.
• what things can affect the rate of a reaction

  -concentration

  -temperature

  -surface area

  -pressure

  -catalyst
• define activation energy


  the minimum energy needed for a successful reaction to occur
• what does the blue line show

  * steep gradient- fast reachtion

  *high volume of gas produced

  
• rate of reaction formulae

  rate= product produced (reactant used up) /time
• how concentration affects rate

  as concentration increases the rate of reaction increases as there are more reactant particles in the same volume so more FREQUENT SUCCESSFUL COLLISIONS
• what experiment is used to test for how concentration affects rate

  -magnesium strip

  -3 different concentration of hydrochloric acid

  -gas syringe

  -stopwatch

  
• how does surface area affect the rate of a reaction

  as surface area increases the rate of a reaction increases as more reactant particles are exposed so more FREQUENT SUCCESSFUL COLLISIONS
• what experiment is used to test for how surface area affects rate

  cotton wool- used to let gas go through but stops acid squirting out

  different sizes of marble chips

  
• how does temperature affects the rate of a reaction

  as temperature increases rate of reaction increases as the reactant particles have more energy so more particles have activation and so more FREQUENT SUCCESSFUL COLLISIONS
• what experiment is used to test for how temperature affects rate

  -measure the time taken for the cross to dissapear with 3 different temperatures

  -cross dissapears because the sulphur produced is solid

  
• define an exothermic reaction

  when heat energy is transferred from the reaction to the surroundings- feels hot
• deine an endothermic reaction

  when heat energy is transferred from the surroundings to the reaction - feels cold
• how do catalysts work

  they provide an alternative pathway with lower activation energy
• how do catalysts affect the rate of a reaction

  adding a catalyst increases the rate of a reaction because particles now hav activation energy and so more FREQUENT SUCCESSFUL COLLISIONS