heat of combustion

The table shows the heat of combustion of three alcohols.

Which of the following factors increases the heat of combustion of alcohols?

• Size of molecules decreases

• Number of carbon atoms per molecule increases

• Number of oxygen atoms per molecule increases

• Number of hydrogen atoms per molecule decreases

The following equation shows the combustion of heptane, C₇H₁₆, in excess oxgen.

C₇H₁₆(l) + 11 O₂(g) → 7 CO₂(g) + 8 H₂O ΔH= -5 512 kJ mol^-

The combustion of heptane in excess oxygen releases 1 378 kJ of energy.

What is the mass of heptane used?

[relative atomic mass of H = 1 and C = 12]

• 25.0 g

• 36.0 g

• 77.0 g

• 88.0 g

The following information shows the results of an experiment to determine the heat change for the combustion of propanol, C₃H₇OH.

Volume of water in the copper container= 300 cm³

Initial temperature of water in copper container=27.5 °C

Highest temperature of water in copper container = 68.5 °C

What is the heat released by the combustion of propanol, C₃H₇OH?

[Specific heat capacity of water = 4.2 J g^-1°C^-1 ; Water density = 1 g cm^-3]

• 34.65 kJ

• 51.66 kJ

• 86.3 kJ

• 120.96 kJ

100 cm³ of water is heated by the burning of a sample of ethanol.

The heat released by the combustion is 10.5 kJ.

What is the maximum increase in temperature of the water?

[Specific heat capacity of water = 4.2 Jg^-1oC^-1]

• 0.025°C

• 0.25°C

• 2.5°C

• 25°C

Diagram 14 shows an energy level diagram for propan-1-ol.

Which of the following sattement is correct about the reaction?

• X kJ of heat is absorbed during the reaction.

• The final temperature is lower than initial temperature.

• The heat of combustion of propan-1-ol is -X kJ/mol

• The total energy content of product is higher than the reactant.

The following is the energy level diagram of a reaction.

Which of the following acids is suitable to replace nitric acid, HNO₃ to obtain the same ΔH value ?

• Ethanoic acid, CH₃COOH

• Carbonic acid, H₂CO₃

• Sulphuric acid, H₂SO₄

• Hydrochloric acid, HCl

In an experiment, 100 cm³ of dilute hydrochloric acid solution is mixed with 100 cm³ sodium hydroxide solution in a polystyrene cup. The concentrations of the two solutions are the same. During the mixing, the temperature of the mixture increased by 7 ⁰C.

What is the heat released in the experiment?

Given that the specific heat capacity of the solution is 4.2 J g^{-1 0}C^-1.

• 1470 J

• 2940 J

• 4410 J

• 5880 J

The reaction between 25.0 cm³ of hydrochloric acid and 25.0 cm³ of sodium hydroxide solution releases the heat of 2100 J.

What is the temperature change of the mixture?

[Specific heat capacity of a solution = 4-2 Jg ^C"1;

Assume that 1 cm³ of a solution is equal to 1 g of the solution]

• 1°C

• 2°C

• 10 °C

• 20 °C

Which process absorbs energy?

• Evaporation

• Combustion

• Neutralisation

• Displacement

Which of the following is an endothermic reaction?

• HCI + NaOH → NaCl + H₂O

• HCI + NaHCO₃ → NaCl + CO₂ + H₂O

• NaCl + AgNO₃ → AgCl + NaNO₃

• Zn + CuSO₄ → ZnSO₄ + Cu