Miscellaneous Flashcards
State Hess’s Law.
The enthalpy change / heat (energy) change (at constant pressure) in a reaction is independent of the route / path taken (and depends only on the initial and final states)
Write a mathematical expression to show how ΔHexp, ΔH1 and ΔH2 are related to eachother by Hess’s Law.
∆Hexp + ∆H2 –∆H1 =0
Hydrazine (N2H4) decomposes in an exothermic reaction. Hydrazine also reacts exothermically with hydrogen peroxide when used as a rocket fuel.Write an equation for the decomposition of hydrazine into ammonia and nitrogen only.
3N2H4 ——->4NH3 + N2
State the meaning of the term mean bond enthalpy.
enthalpy / heat (energy) change / required / neededto break / dissociate a covalent bond (or a specified covalentbond)average / mean over different molecules / compounds / substances
Nitrogen monoxide (NO) catalyses the decomposition of ozone into oxygen. Write the overall equation for this decomposition.
2O3—————-> 3O2
Use the overall equation to deduce Step 3 in the following mechanism that shows how nitrogen monoxide catalyses this decomposition.Step1 O3 ——->NO + O2 Step2 NO + O3 ———>NO2 + O2Step 3 …………………………………………………………………………………………………………………..
O + NO2 ———->NO + O2
Concentrated sulfuric acid reacts with solid potassium iodide as shown in the equation. 8KI + 9H2SO4 ——–>4l2 + 8KHSO4 + H2S + 4H2OGive two observations that you would make when this reaction occurs.In terms of electrons, state what happens to the iodide ions in this reaction.State the change in oxidation state of sulfur that occurs during this formation of H2S and deduce the half-equation for the conversion of H2SO4 into H2S
Any two from• purple vapour/gas• (white solid goes to) black or black/grey or black/purplesolid• bad egg smell or words to this effectThe iodide ion(s) / they lose (an) electron(s) OR 2I– ——>I2 + 2e–Oxidation state of S changes from +6 to –2 or changes by 8H2SO4 + 8H + 8e- ———->H2S + 4H2OORSO4(2-) + 10H(+) + 8e- ———-> H2S + 4H2O
State why the standard enthalpy of formation for hydrogen gas is zero.
It is an element / elemental
State and explain what happens to the yield of methanol when the total pressure is increased in this synthesis.CO2(g) + 3H2(g)  CH3OH(g) + H2O(g)
(The yield) increases / goes up / gets more because there are more moles / molecules (of gas) on the left / of reactants
State the meaning of the term carbon-neutral.
An activity which has no net / overall (annual) carbon emissions to the atmosphere
The manufacture of food grade phosphoric acid for use in cola drinks begins with the production of pure white phosphorus from the mineral fluoroapatite, Ca5F(PO4)3Complete the following equation for the manufacture of phosphorus………Ca5F(PO4)3 + 9SiO2 + ……..C ———->9CaSiO3 + CaF2 + ……..CO + ……..P
2Ca5F(PO4)3 + 9SiO2 + 15C——————>9CaSiO3 + CaF2 +15CO + 6P
As the phosphorus cools, it forms white phosphorus, P4Give the oxidation state of phosphorus in each of the following. P4 …………………………………………………….H3PO4 ………………………………………………
(P4 =) 0(H3PO4 =) (+) 5
State the meaning of the term catalyst.
A substance that speeds up a reaction OR alters / increases the rate of a reaction AND is chemically unchanged at the end / not used up.
State the meaning of the term hydration.
The addition of water (QoL ) to a molecule / compound
Write an equation for the hydration of propene to form isopropyl alcohol. Give the IUPAC name for isopropyl alcohol.Equation ……………………………………………………………………………………………………………..IUPAC name ……………………………………………………………………………………………………….
CH3CH=CH2 + H2O —–> CH3CH(OH)CH3 (C3H6)propan-2-ol
There are many uses for compounds of barium.Write an equation for the reaction of barium with water.
Ba + 2H2O ———-> Ba(OH)2 + H2
State the trend in reactivity with water of the Group 2 metals from Mg to Ba
(Reactivity with water) increase(s) / increasing / increased (down the Group / from Mg to Ba)
State how barium sulfate is used in medicine.Explain why this use is possible, given that solutions containing barium ions are poisonous.
Barium meal / barium swallow / barium enema or (internal) X-ray or to block X-raysBaSO4 / barium sulfate is insoluble (and therefore not
Give the formula of the least soluble hydroxide of the Group 2 metals from Mg to Ba
Mg(OH)2
State the meaning of the term stereoisomers.
Compounds / molecules with) the same structural formula with atoms/bonds/groups arranged differently in space
The reaction of butane-1,4-diol with butanedioic acid produces the polymer PBS used in biodegradable packaging and disposable cutlery.Butanedioic acid is produced by two different processes.Process 1Aqueous sodium hydroxide reacts with 1,4-dibromobutane to make butane-1,4-diol. Butane-1,4-diol is oxidised to butanedioic acid.Process 2Glucose reacts with carbon dioxide in the presence of microorganisms to produce butanedioic acid directly.The carbon dioxide used in this process is obtained from a local factory that produces bioethanol.8 (a)Deduce one safety reason and one environmental reason why Process 2 is preferred to Process 1.
- Safety (in Process 1)Sodium hydroxide / alkali is corrosive / harmful / caustic or sodium hydroxide is alkali(ne)ORBromine compounds are toxic / poisonous2. EnvironmentalProcess 2 could be used as a carbon sink / for carbon captureORuses waste / recycled CO2 / CO2 from the factory / CO2 from the bioethanol (or biofuel) productionORreduces or limits the amount of CO2 released / given out (into the atmosphere)ORProcess 2 uses renewable glucose / renewable resource(s)
Name the mechanism for the following reaction that occurs in Process 1. BrCH2CH2CH2CH2Br + NaOH———> BrCH2CH2CH2CH2OH + NaBr
nucleophilic substitution
The silicon chip industry requires the production of pure silicon. Silicon is extractedfrom its ore, silicon dioxide (SiO2), by a process similar to that used in the extraction oftitanium.Write an equation for the formation of SiCl4 from SiO2 using chlorine and carbon.Suggest how the liquid SiCl4 is purified.
SiO2 + 2Cl2 + 2C——–> SiCl4 + 2CO(fractional) distillationORgas (-liquid-) chromatography (GLC)
The final stage in the extraction of silicon involves the use of hydrogen gas to convertthe SiCl4 into silicon and hydrogen chloride.Write an equation for this reactionState the role of hydrogen in this reaction.Give one risk associated with the use of hydrogen gas.
SiCl4 + 2H2 ——–>Si + 4HClReducing agent Explosion / explosive
The magnesium used to make magnesium ferrosilicon alloys is extracted frommagnesium oxide using silicon.Write an equation for this reaction to produce magnesium and silicon dioxide.
2MgO + Si ——->2Mg + SiO2
The rate of a chemical reaction is influenced by the size of the activation energy. Catalysts are used to increase the rates of chemical reactions but are not used up in the reactions.Give the meaning of the term activation energy (2)
The activation energy is the minimum / least / lowest energy (energy) for a reaction to occur / to go / to start(i.e. for an effective collision)
Explain how a catalyst increases the rate of a reaction (2)
Catalysts provide an alternative route for a reactionANDLowers the activation energy
For each of the following reactions, identify a catalyst and name the organic product of the reaction.The fermentation of an aqueous solution of glucose.The hydration of but-2-ene.
yeast or zymase ethanol(Concentrated) H2SO4 butan-2-ol
Write an equation for the reaction in which the enthalpy change is the standard enthalpy of formation of gaseous methoxymethane, CH3OCH3
2C(s) +1⁄2O2(g) +3H2(g)—–> CH3OCH3(g)
Define the term standard enthalpy of combustion.
Enthalpy / heat(energy) change when 1 mole of substance; Is completely burned in oxygen / burned in excess oxygen;Under standard conditions /100kPa and 298K
State why the standard enthalpy of formation of oxygen is zero.
It is an element / (by) definition
Suggest which bond is most likely to break first in a collision between a methoxymethane molecule and a hydrogen iodide molecule.
H – I bond
Chemists supported the legislation to ban the use of CFCs. Modern refrigeratorsuse pentane rather than CFCs as refrigerants.With reference to its formula, state why pentane is a more environmentally acceptable refrigerant.
Any one ofPentane does not contain chlorine OR C–Cl (bond) Pentane is chlorine-freeORPentane does not release chlorine (atoms / radicals)
With reference to the Maxwell–Boltzmann distribution, explain why an increase in temperature increases the rate of a chemical reaction.
Increase in the number / proportion of molecules with E ≥ Eacreatingwait for it Saskia…….More effective / productive / successful collisions
The following pairs of compounds can be distinguished by observing what happens in test-tube reactions.For each pair, give a suitable aqueous reagent that could be added separately to each compound.Describe what you would observe in each case. NaF(aq) and NaCl(aq)Reagent Observation with NaF(aq) Observation with NaCl(aq)
NaF(aq) and NaCl(aq)M1 AgNO3 OR silver nitrate OR any soluble silver saltM2 remains colourless or no reaction or no (observed) change or noprecipitateM3 white precipitate or white solid / white suspension
The following pairs of compounds can be distinguished by observing what happens in test-tube reactions.For each pair, give a suitable aqueous reagent that could be added separately to each compound.Describe what you would observe in each case. BaCl2(aq) and MgCl2(aq)Reagent Observation with BaCl2(aq)Observation with MgCl2(aq)
BaCl2(aq) and MgCl2(aq) any soluble sulfate by name or formula e.g. sodium sulfate or sulfuric acid.M2 white precipitate or white solid / white suspensionM3 remains colourless or no reaction or no (observed) change or noprecipitateOR as an alternativeM1 NaOH / KOHM2 remains colourless or no reaction or no (observed) change M3 white precipitate or white solid / white suspension
The following pairs of compounds can be distinguished by observing what happens in test-tube reactions.For each pair, give a suitable aqueous reagent that could be added separately to each compound.Describe what you would observe in each case. AgCl(s) and AgI(s)Reagent Observation with AgCl(s) Observation with AgI(s)
M1 ammonia (can be dilute or concentrated)M2 dissolves OR soluble OR (forms a) colourless solution OR goescolourlessM3 does not dissolve OR not soluble Or remains as a solid OR no (observed) change OR no reaction OR yellow solid remainsOR if concentrated ammonia has been used, accept yellow solid turns white.OR as an alternative using conc sulfuric acidM1 concentrated sulfuric acid OR c(onc) H2SO4M2 misty / white fumes / gasOR remains whiteOR no change (in colour)M3 turns black (solid)OR purple fumes / gasOR correct reference to H2S observation (e.g. bad egg smell)
The following pairs of compounds can be distinguished by observing what happens in test-tube reactions.For each pair, give a suitable aqueous reagent that could be added separately to each compound.Describe what you would observe in each case.Butan-2-ol(l) and 2-methylpropan-2-ol(l)Reagent Observation with butan-2-ol(l) Observation with 2-methylpropan-2-ol(l)
M1 acidified potassium dichromate or K2Cr2O7/H2SO4OR K2Cr2O7/H+ OR acidified K2Cr2O7M2 (orange to) green solution OR goes greenM3 (solution) remains orange or no reaction or no (observed) change Alternative using KMnO4/H2SO4M1 acidified potassium manganate(VII) or KMnO4/H2SO4OR KMnO4/H+ OR acidified KMnO4M2 colourless solution OR goes colourlessM3 (solution) remains purple or no reaction or no (observed) change
The student carried out a laboratory experiment to determine the enthalpy change when a sample of butan-1-ol was burned.The student found that the temperature of 175 g of water increased by 8.0 oC when 5.00 x 10–3 mol of pure butan-1-ol 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 butan-1-ol is burned.(The specific heat capacity of water is 4.18 J K–1 g–1)
M1 q = m c ΔT OR calculation 175 x 4.18 x 8M2 = 5852 (J) OR 5.85 (kJ) OR 5.9 (kJ) (This also scores M1) M3 0.005 mol, therefore ΔH = –1170 (kJmol-1)OR ΔH = –1170.4 (kJmol-1) OR ΔH = –1200 (kJmol-1)
A scientist used mass spectrometry to analyse a sample of the air near a fertiliser factory. The sample of air included traces of a gas which was shown by its molecular ion to have a precise Mr = 44.00105State the meaning of the term molecular ion.
The molecular ion is the molecule with one / an electron knocked off / lostIt has a single +ve chargeand has the highest m/z ratio
State why the precise relative atomic mass for the 12C isotope is exactly 12.00000
By definition
Give a use for magnesium hydroxide in medicine.
to neutralise stomach acidityORas an antacidOReases indigestion / heartburn
Calcium carbonate is an insoluble solid that can be used in a reaction to lower the acidity of the water in a lake.Explain why the rate of this reaction decreases when the temperature of the water in the lake falls (3)
Decrease in T decreases the energy of the particles / ions / H+ / moleculesDecrease in the number of / less particles / ions / H+ / molecules with E ≥ EAct or E ≥ minimum energy to react*Few(er) / Less effective / productive / successful collisions
Strontium metal is used in the manufacture of alloys.Explain why strontium has a higher melting point than barium.
Strontium has a higher melting point than barium, because size of cations/proximity of electronsi.e.delocalised electrons closer to cations / positive ions / atoms / nucleusRelative strength of metallic bondingi.e. (Sr) has stronger attraction between the cations / positive ions / atoms / nucleus and the delocalised electronsORstronger metallic bonding(assume argument refers to Sr but accept converse argument for Ba)
Write an equation for the reaction of strontium with water.
Sr + 2H2O —–> Sr(OH)2 + H2
Magnesium can be used in the extraction of titanium.Write an equation for the reaction of magnesium with titanium(IV) chloride.
2Mg + TiCl4 ——–>2MgCl2 + Ti
