Qualification > Sciences

chemistry

<< < (5/7) > >>

tmisterr:
b ii Q=m*c*change in temp so 12.2*4.2*200=10248 j
b iii 10.248kj is the enthalpy change when 1 g of calcium is dissolved, but one mole of calcium is 40.1g  so 40.1*10.248=410.9 = 411 kj mol-1
c ii you need to use a hess cycle
      We know the enthalpy change of the reaction to form Calcium Hydroxide and Hydrogen (calculated in biii) and we have been given the enthalpy change of formation of water.
                       
                               Ca + 2H2O ----> Ca(OH)2 + H2

                                                     
                                              Ca + 2H2 + O2

so applying Hess law, starting from the lower equation, you can either first form calcium and water then form calcium hydroxide or directly form Calcium Hydroxide(this is the enthalpy change we are looking for). therefore:
                    2*-286+-411= enthalpy change of formation of Calcium hydroxide = -983kj mol-1

d) mole ratios (from equation in b)
 1 mole of calcium forms one mole of hydrogen so 1/40.1 moles of calcium will form 1/40.1 moles of hydrogen.
so volume of oxygen is 1/40.1 * 24= 0.5985 dm3 or 598.5 cm3

ruby92:
28) D agn
monosubstituted alkene, one R group is attached to the carbon-carbon double bond. Not oxidized by mild oxidising agents

could you explain this a bot further please?

chanella:
http://www.a-levelchemistry.co.uk/AQA%20AS%20Chemistry/Unit%201/1.5%20Introduction%20to%20Organic%20Chemistry/1.5%20home.htm

This website has notes,worksheets, tests

ruby92:


Thank You ppl :D

ruby92:
o/n 2008 paper 1
4 9 13 19 39(how is 2 correct) 32 ( water acts as a base rite?) 29 (why not A), 26(why not B)

Navigation

[0] Message Index

[#] Next page

[*] Previous page