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AQA AS General Unit2

QuestionAnswer
State Le Chatelier’s principle. When a system/reaction in equilibrium is disturbed, the equilibrium shifts in a direction which tends to reduce the disturbance
State the meaning of the term enthalpy change. Heat (energy) change at constant pressure
State Hess’s Law. The enthalpy change for a reaction is the same,whatever the route taken from reactants to products
State the meaning of the term reducing agent. A reducing agent is an electron donor
Write equations for the following steps in the mechanism for the reaction of chlorine with ethane to form chloroethane (CH3CH2Cl). Initiation Cl2 2Cl• First propagation Cl• + CH3CH3 -->•CH2CH3 + HCl C2H6 Second propagation Cl2 + •CH2CH3 -->CH3CH2Cl + Cl• C2H5Cl Termination 2 •CH2CH3 -->CH3CH2CH2CH3
Give the meaning of the term standard enthalpy of combustion. The enthalpy change of combustion when one mole of substance is completely burned in oxygen under standard conditions
Give the meaning of the term activation energy. The activation energy is the minimum for a reaction to occur
Explain how a catalyst increases the rate of a reaction. Catalysts provide an alternative route for a reaction to occur which has a lower activation energy
State how, if at all, the value of the most probable energy (Emp) changes as the total number of molecules is increased at constant temperature. Stays the same
State how, if at all, the number of molecules with the most probable energy (Emp) changes as the temperature is decreased without changing the total number of molecules. Increases
State how, if at all, the number of molecules with energy g rea ter than the activation energy (Ea) changes as the temperature is increased without c hanging the total number of molecules. Increases
State how, if at all, the area under the molecular energy distribution cur ve changes as a catalyst is introduced without changing the temperature or the total number of molecules. Stays the same
Define the term standard enthalpy of formation. The enthalpy change when one mole of compound is formed from its elements under standard conditions
Identify one environmental problem and identify one use for the sulfur dioxide. Environmental problem--> Acid rain Use--> Used to make sulfuric acid/plaster board
Give two features of a reaction at equilibrium. Concentrations remain the same Forward rate equals backward rate
Explain why a catalyst has no effect on the position of an equilibrium. Catalysts speed up both forward and reverse reactions It increases the rate but speed is the same
Explain why a small increase in temperature has a large effect on the initial rate of a reaction. A small increase in temperature results in a much higher proportion of collisions with E ≥ Eact and energy is greater than the activation energy
In the production of bioethanol, glucose (C6H12O6) is converted into a dilute aqueous solution of ethanol and carbon dioxide. Give the name of this process and state three essential conditions necessary to produce a good yield of ethanol. Fermentation Three conditions: (enzymes from) yeast 25°C ≤ T ≤ 42°C No air
Increasing the conc. of reactants ... Moves to the right More products
Decreasing the conc. of reactants ... Moves to the left More reactants
Increasing the conc. of products... Moves to the left More reactants
Decreasing the conc. of products... Moves to the right More products
Increasing the pressure... Moves to the side with fewer gas molecules
Decreasing the pressure ... Moves to the side with more gas molecules
Increasing the temperature... Moves in the endothermic reaction +ive
Decreasing the temperature... Moves in the exothermic reaction -ive
Most collisions do not lead to reactions because then need the right orientation and the right amount of energy
Identify a suitable catalyst for the production of ethanol Identify the type of reaction. Give two conditions that will produce a high yield of ethanol. Concentrated phosphoric acid Hydration or electrophilic addition • Excess ethene or Excess steam • Pressure 6500 kPa • High Temperature 570K
What is methanol used for? In relation to Le Chatelier's principle It is a starting material for making other chemicals Plastics like terylene/Bakelite and motor fuel low temperature and high pressure gives a larger yield, at 500K and 10000kPa
Created by: luvingmusic