topic 5 exam qs for 5.1.1

• from the results the student concludes that the rate equation is rate = k[S2O3 2- (aq)]

  explain how the students results support this rate equation

  from experiment 1 and 2, as [S2O3 2-] x 1/2, rate also x 1/2

  so first order for S2O3 2-

  from experiment 2 and 3 [S2O3 2-] x 1/4, [H+] x 1/2, rate x 1/4

  so zero order for H+
• from the graph the student estimates the value of lnA as -2.00 (A is the pre-exponential factor)

  explain what the mistake the student has made

  x-axis does not start at zero

  so y-intercept does not equal a
• the student calculates the value of k in investigation 1 as 0.075 s-1

  determine the temp in degrees celsius at which investigation 1 was carried out

  lnk = ln(0.075) = -2.59

  1/T = 3.1 x 10-3

  1/3.1 x 10-3 = 322.6 K

  convert kelvin into celsius

  322.6 - 273 = 47.6 degrees celsius
• lnk = -Ea/R • 1/T + lnA

  y = m x + c