C2

Rates and Energy

definition for rate of reaction

–Speed at which a chemical reaction takes place

To work out the rate of reaction between 30-60s:

• 60-30= 30

• 45-25 =20

• 20/30 =0.66 cm3/s

Open Ended

What factors affect the rate of reaction?

ANSWERS

• Surface area

• Temperature

• Concentration

• Pressure

• Catalysts

Endo & Exo

• exothermic reactions release energy to their surroundings – they get hot

• endothermic reactions absorb energy from their surroundings – they get cold.

• Most chemical reactions are exothermic

Rules when naming salts

• Name of the metal goes first

• Look at the formulae for the acid. Does it contain Oxygen?

• HCl - no Oxygen = chlorIDE

• H2SO4 - with Oxygen = SulphATE

electrolysis and electroplating

RULES!!!!!!

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  1. At the negative electrode (cathode): If the metal is above Copper in the reactivity series, Hydrogen gas is formed.

  
  

• 2. At the positive electrode (anode): If the non-metal is a halogen (group 7) then the halogen gas is formed. If it is not a halogen, Oxygen gas is formed

balancing the half equations

• Cu²⁺    Cu

  (Cu²⁺ + 2e   Cu)

• H⁺       H₂

  (2H ⁺ - 2e         H₂)

electroplating

• Covering an object with a thin coating of metal during an electrolysis reaction.

  The object to be plated is in the negative electrode in the electrolysis cell e.g electroplating an object with silver.

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1.Silver atoms lose electrons at the positive electrode to form Ag⁺ ions (Oxidation)

2.Ag⁺ move through silver nitrate solution to the negative electrode

3.Ag⁺ ions gain electrons at the negative electrode to become Ag atoms

4.Ag atoms are deposited on the object being electroplated

At the positive electrode: Ag – e       Ag⁺

At the negative electrode:  Ag⁺ + e          Ag 

equation

What is the half equation at….

1.The negative electrode: Al3+ + _____ -> _______

2.The positive electrode: 2O2- -_____-> ______