C7 PPQ Mistakes
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In an energy change diagram what is the overal energy change and the activation energy?
• Activation = distance between reactants and top of the curve • Overall energy change = distance between the energy of reactants and products
If reactants and products are given in the question what do use them for in energy change diagram
• You use them to label the reactants and products • instead of just writing ‘reactant’ and ‘product’
How to improve investigation: • Measure temp of 100cm3 of water • Add 10 g of ammonium nitrate • Stir once • Measure the temp of the solution every minute for 7 min
• Stir more times • Use a digitial thermomter • Insulate the cup • Use a large man of ammonium nitrate • Use a smaller volume of water
Why does the temperature of the reaction between ammonium nitrate + water decreases then increases
• Reaction is endothermic • After the reaction is finished energy is transferred to the solution
Why leave a solution for 3 minutes before adding the other reactant
• To reach room tempertaure • To reach constant temperature
Why does a reaction have an increase in temperature and then a decrease
• Reaction is exothermic • after reaction is finished • energy is lost to surroundings
A student is investigating the energy change of a endothermic reaction They use a thermometer and a glass beak How can you make the experiment more accurate
• Polysterene cup isntead of glass • so that energy would not be gained
Two advantages of using fuel cells instead of rechargable cells for cars
• travel further before refueling • They are faster to refuel
How can you reduce volume
• Compress it in a high pressure gas compressor
Explain the temperature of an endothermic reaction to which an excess is added
• As the reaction progress the temperature lowers • as energy is taken in • As the solute is at room temperature the solution begins to rise
endothermic reaction is polystyrene cup vs in metal cup
• metal is a heat conductor • reaction is endothermic • so allows energy to move into the solution metal = higher temp of solution
why will using a polystyrene cup grant more accurate results thatn a glass cup
• Polystyrene is a better thermal insulator • less energy would be transferred to the environment
random error for energy change practical
• stirring different amounts • different starting temperatures
how to investigate the effect of concentration of voltage (use 1 mol/dm3 of NaCl)
• Place one nickel electrode and one (metal) electrode • Use an electrolyte of 1 mol/dm3 of NaCl • meausre out 10cm3 using a meauring cylinder • meaure the voltage using a voltmeter • keep the volume of the electrolyte the same but add 2cm3 of water • measure using pipette • to dilute the solution • keep the volume of the electrolyte the same but add 4cm3 of water • measure using pipette • to dilute the solution
where does is the activation energy on a graph
• from the products • to the peak