Chemistry unit 2 wjec 2016

Question 1

What type of reaction is photosynthesis?

Answer 1

Exothermic

Question 3

2 methods which student could use to follow rate of reaction?

Answer 3

use a colorimeter to measure colour changes with time
use a pH meter to measure pH with time
use a balance to measure mass changes with time

Question 4

Which feature of a molecule gives rise to EZ isomerism?

Answer 4

presence of a carbon to carbon double bond

Question 5

Why does the below molecule show E-Z isomerism?

Answer 5

No
2 of the groups one of the double bonded carbon atoms are the same

Question 6

Equation for copper oxide reacts with aqueous ethanoic acid?

Answer 6

CuO + 2HCOOH —- (HCOO)2Cu+ H2O

Question 7

Calculate enthalpy change for the reaction?

Answer 7

Q= 25 x 4.18 x 14.5 = 1515J
moles mg = 0.1/24.3 = 4.12 x 10^-3

delt H = 1515/4.12 X 10^-3 = -368 kjmol-1

Question 8

Why Efan obtain a different value for delta H?

Answer 8

n(mg) = 8.23 x 10^-3
1.64 x 10^-2 moles HCl for all o react
n(HCl) = 5x10^-3
not enough for complete reaction

Question 9

Maximum percentage error in the mass of magnesium she used?

Answer 9

max reading in 1 reading taken = 0.05g
0.05/0.01 x 100 = 50%

Question 10

Why can this reaction not be used to measure enthalpy change for the reaction that forms magnesium chloride from magnesium?

Answer 10

cant measure delta H
only delta T

Question 11

Definition of standard enthalpy change of combustion?

Answer 11

enthalpy change when 1 mole of a substance is burned in excess oxygen under standard conditions

Question 12

Avergae bond enthalpy?

Answer 12

bonds broken - bonds formed

Question 13

Why bond enthalpies are described as being average bond enthalpies?

Answer 13

average used since each individual bond will be in a different environment and therefore have different strengths