Analysis and Results of Enthalpy Change

Analysis and Results of Enthalpy Change

ALCOHOL

AVERAGE MASS BURNT (G)

METHANOL

1.54

ETHANOL

1.02

PROPAN-1-OL

0.77

BUTAN-1-OL

0.69

PENTAN-1-OL

0.55

HEXAN-1-OL

0.52

Following the gathering of results, the enthalpy change of combustion

of the alcohols was calculated using the equation from page 2:

Energy Transferred = Mass of water x Temperature rise x specific heat

capacity (4.17)

Now to calculate the enthalpy change of combustion, the following

steps are taken:

1.) Energy per gram = Energy Transferred ÷ Average mass change of

alcohol

2.) Energy per mole = Energy per gram x Molecular mass

The Energy Transferred from each alcohol is constant as the variables,

volume of water (200ml) and temperature rise (15oC) were kept

constant. Therefore the calculation of energy transferred from each

alcohol is:

Energy Transferred = cm∆T

= 4.17 x 200 x 15

= 12510 J

To convert this into KJ, we divide it by 1000 = 12510 ÷ 1000 = 12.510

KJ.

Hence 12.510 KJ of energy is transferred by each alcohol to raise

200ml of water by 15oC.

The calculations of the enthalpy change of combustion for each alcohol

can be seen on the following page.

1.) Methanol – CH3OH : molecular mass = 32g

Energy per gram = Energy Released ÷ Average mass change

= 12.510 ÷ 1.54

= 8.10 KJ

Energy per mole = Energy per gram x molecular mass

= 8.10 x 32

= 259 KJ mol -1

2.) Ethanol – CH3CH2OH : molecular mass = 46g

Energy per gram = Energy Released ÷ Average mass change

= 12.510 ÷ 1.