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A quantity of 1.922 g of methanol (ch3oh) was burned in a constant-volume bomb calorimeter. consequently, the temperature rose by 5.14°c. if the heat capacity of the bomb plus water was 8.69 kj / °c, calculate the molar heat of combustion of methanol.

Respuesta :

barnuts

The formula for calculating the amount of energy or heat released is:

ΔH = C ΔT

where ΔH is heat of combustion, C is heat capacity, while ΔT is change in temperature

 

ΔH = 8.69 kJ / °C * (5.14°C)

ΔH = 44.67 kJ

 

Then we calculate the moles of CH3OH which has molar mass of 32.04 g/mol:

moles = 1.922 / 32.04 = 0.05999 mol

 

SO the molar heat of combustion is:

ΔHm = 44.67 kJ / 0.0599875 mol

ΔHm = 744.60 kJ / mol

The molar heat of combustion of methanol is -745kJ/mol

Molar Heat of Combustion

This is heat released to the environment when one mole of a substance in this case methanol is completely burned.

Data given;

  • Mass of methanol = 1.922g
  • Change in temperature = 5.14° C
  • Heat capacity of the bomb calorimeter + water = 8.69kJ/°C

Number of moles

The number of moles of methanol is the ratio between the mass to the molar mass of methanol

  • mass = 1.922g
  • molar mass = 32g/mol

[tex]n=\frac{m}{M}\\n=\frac{1.922}{32}\\n=0.06moles[/tex]

The number of moles present in 1.922g of methanol is 0.06moles.

Heat of combustion

This is the heat required to completely burn a substance

[tex]Q=mc[/tex]ΔT

[tex]Q=8.69*5.14=44.67kJ[/tex]

Molar Heat of Combustion

ΔH = [tex]-(\frac{Q}{n})[/tex]

n = number of moles

ΔH = [tex]-\frac{44.7}{0.06}=-745kJ/mol[/tex]

The molar heat of combustion is -745kJ/mol

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