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Edexcel Jan 2015 (IAL) Paper 1 Q22
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![Question Number 22(a) Question Number 22(b)(i) Question Number 22(b)(ii) Acceptable Answers Reject 1st markidea of moles / amounts specified (Enthalpy change when) the number of moles of reactants ALLOW (Enthalpy change when) the number of moles of products or substances / just molar quantities / just amounts / just moles (1) 2nd markidea of an equation (react as specified in the balanced) equation (1) IGNORE references to (standard) conditions / just enthalpy change that occurs during a reaction Acceptable Answers (Heat energy absorbed = 100 x 4.2 x 5.5 =) 2310 (J) ALLOW 2.3(10) kJ IGNORE sign and sf except one sf Acceptable Answers (Moles NH4CNS = 15.22 =) 0.2(00) (mol) 76.1 IGNORE sf ALLOW Mr = 76 for NH4CNS to give 0.200(3) (mol) Mark One mole of reactants / One mole of products for 1st mark Reject Mark Reject Mark WCH0101 1501<br />
Acceptable Answers Question Number 22(b)(iii) Hreaction = +2.3(10) x2 = +23.1 (kJ mol-1) 0.2(00) = +23 (kJ mol1) to 2 sf First markcorrect computation of Hreaction: 2 x [answer to (b)(i) in kJanswer to (b)(ii) in mol] Second markstand alone, for correct rounding: A final answer to two sf Third markstand alone, for giving a + sign for endothermic reaction: + sign in front of final answer NOTE: +12 (kJ mol1) scores (2) (i.e. the 2nd and 3rd marks) Reject Mark Incorrect units given by the candidate (no 3rd scoring point) (1) (1) (1) Mark WCH0101 1501 Acceptable Answers Reject (Average amount of) energy/enthalpy required to break one mole of (covalent) bonds ALLOW Energy change/enthalpy change to break one mole of (covalent) bonds (1) (in the) gas / gaseous (state) (1) Energy/enthalpy released OR Bonds formed/made OR 1 mol of compound for 1st mark Question Number 22(c)(i)<br />
Acceptable Answers Question Number 22(c)(ii) For a pi/-bond: Reject Mark Sideways overlap of p-orbitals / overlap of p- orbitals above and below stated or drawn on a diagram (1) For a sigma/-bond: Head-on overlap of any orbitals, stated or drawn on a diagram (1) MAX (1) if it is not specified/clear which type of overlap relates to which type of bond IGNORE Incorrect diagram NOTE JUST 1st diagram below scores (1) whereas JUST 2nd diagram below scores (2)-bond -bond OR-bond-bond -bond NOTE: For the -bond, allow any form of end-on overlap of orbitals MAX (1) if only an UNLABELLED but otherwise correct diagram is given (ie also no words) WCH0101 1501<br />
Mark Reject -bond is stronger than the -bond OR C=C bond weaker than C-C bond Acceptable Answers Question Number 22(c)(iii) -bond is weak(er) OR -bond is strong(er) OR The sideways overlap is less effective than the head-on overlap ALLOW The two bonds in the (C=C) double bond are not the same strength IGNORE References to C=C bond more reactive than C-C bond / restricted rotation Question Number 22(c)(iv) Reject Mark Acceptable Answers [FIRST, check the answer on the answer line IF answer = 1936 (kJ mol1) award (3) marks; +1936 (kJ mol1) scores (2)] Bonds broken (6 x (CH) = 6 x 413 + 1 x (CC) = 1 x 347 + 1 x (C=C) = 1 x 612 + 4 x (O=O) = 4 x 498 =) (+)5678 (1) Bonds made (6 x (C=O) = 6 x 805 + 6 x (OH) = 6 x 464 =) ()7614 (1) Hreaction = bonds broken + bonds made = (+)5678 + ()7614 = 1936 (kJ mol1) (1) NOTE 3rd mark CQ on answers calculated for bonds broken and bonds made WCH0101 1501<br />
Question Number 22(c)*(v) Under standard conditions/298 K water is Acceptable Answers Reject Mark a liquid OR (Calculations involving) bond energies refer to (water in) gaseous state (1) Energy released/given out on changing from gas to liquid OR Energy absorbed/taken in on changing from liquid to gas (1) ALLOW max (1) if state that bond energies are average values (from a range of compounds) IGNORE References to heat losses / incomplete combustion (Total for Question 22 = 17 marks) WCH0101 1501<br />](https://learnah.org/wp-content/uploads/2018/08/January_2015_IAL_MS_-_Unit_1_Edexcel_Chemistry_A-level_22-0.jpg)
