Alcohols Flashcards
Ethanol is an important industrial compound.Ethanol can be produced by the hydration of ethene. The equation for the equilibrium that is established isH2C=CH2(g) + H2O(g) CH3CH2OH(g) ΔH = – 42 kJ mol–1The operating conditions for the process are a temperature of 300 oC and a pressure of 7 MPa.Under these conditions, the conversion of ethene into ethanol is 5%.Identify the catalyst used in this process.Deduce how an overall yield of 95% is achieved in this process without changing the operating conditionsUse your knowledge of equilibrium reactions to explain why a manufacturer might consider using an excess of steam in this process, under the same operating conditions.
c(oncentrated) phosphoric acid / c(onc.) H3PO4 OR c(oncentrated) sulfuric acid / c(onc.) H2SO4Re-circulate / re-cycle the (unreacted) ethene (and steam) / the reactantsOR pass the gases over the catalyst several / many times
H2C=CH2(g) + H2O(g) CH3CH2OH(g) Use your knowledge of equilibrium reactions to explain why a manufacturer might consider using an excess of steam in this process, under the same operating conditions.
(By Le Chatelier’s principle) the equilibrium is driven / shifts / moves to the right / L to R / forwards / in the forward directionandThe equilibrium moves / shifts to• oppose the addition of / increased concentration of / increasedmoles/ increased amount of water / steam• to decrease the amount of steam / waterYield of product / conversion increase OR ethanol increases / goes up / gets more
At pressures higher than 7 MPa, some of the ethene reacts to form a solid with a relative molecular mass greater than 5000Deduce the identity of this solid.Give one other reason for not operating this process at pressures higher than 7 MPa.Do not include safety reasons.
Poly(ethene) / polyethene / polythene At higher pressures it costs more / higher cost of electrical energy to pump / pumping costORCost of higher pressure equipment / valves / gaskets / piping etc. OR expensive equipment
Write an equation for the reaction that has an enthalpy change that is the standard enthalpy of formation of ethanol.
2C(s / graphite) + 3H2(g) + 1⁄2O2(g)——> (C2H5OH)(l)
When ethanol is used as a fuel, it undergoes combustion. Define the term standard enthalpy of combustion.
The enthalpy change / heat change at constant pressure when 1 mol of a compound / substance / elementis burned / combusts / reacts completely in oxygen OR burned / combusted / reacted in excess oxygenwith (all) reactants and products / (all) substances in standard / specified states
Gaseous ethanol can be used to convert hot copper(II) oxide into copper. Deduce the role of ethanol in this reaction.
Reducing agent OR reductant OR electron donor OR to reduce the copper oxide
In the absence of oxygen, an aqueous solution of glucose can be fermented to produce ethanol for use in alcoholic drinks.Write an equation for this fermentation reaction.Give two other essential conditions for the production of ethanol in this fermentation.
C6H12O6 ———>2CH3CH2OH + 2CO21. (enzymes from) yeast or zymase2. 25oC≤T≤42oC OR 298K≤T≤315K
The fermentation of glucose from crops is the main method for the production of ethanol. The product is called bioethanol. The European Union has declared that bioethanol is carbon-neutral.State the meaning of the term carbon-neutral.
An activity which has no net / overall (annual) carbon emissions to the atmosphere / air
Other than carbon-neutrality, state the main advantage of the use of glucose from crops as the raw material for the production of ethanol.
Renewable / sustainable not greenhouse gases or global warming
Give 3 disadvantages of the use of crops for the production of ethanol.
Subject to weather / climateORDepletes food supply OR the land use for (specified) foodORRequires use of / uses more fossil fuels
Write an equation for the complete combustion of methanol.
CH3OH + 11⁄2O2————–> CO2 + 2H2O
A student carried out an experiment to determine the enthalpy change when a sample of methanol was burned.The student found that the temperature of 140 g of water increased by 7.5 oC when 0.011 mol of methanol was burned in air and the heat produced was used to warm the water.Use the student’s results to calculate a value, in kJ mol–1, for the enthalpy change when one mole of methanol was burned.(The specific heat capacity of water is 4.18 J K–1 g–1)
M1 q=m c ΔTOR q =140 x 4.18 x 7.5M2 = 4389 (J) OR 4.389 (kJ) OR 4.39 (kJ) OR 4.4 (kJ) (also scores M1)M3 Using 0.0110 moltherefore ΔH = – 399 (kJmol-1 ) OR – 400
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.
fermentationThree conditions in any order M2 (enzymes from) yeast or zymaseM3 25°C ≤T≤42°C OR 298K≤T≤315K M4 anaerobic / no oxygen / no air OR neutral pH
State the class of alcohols to which ethanol belongs.
Primary alcohol
State three essential conditions for the fermentation of aqueous glucose to form ethanolwrite an equation for the reaction
M1 yeast or zymaseM2 30 oC ≥T≤42oCM3 anaerobic / no oxygen / no air OR neutral pHC6H12O6 ——> 2C2H5OH + 2CO2
