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