click below
click below
Normal Size Small Size show me how
AQA AS General Unit2
Question | Answer |
---|---|
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 |