Thermochemistry

In which of the chemical reactions releases heat to the surroundings?

• Dissolving potassium nitrate in water

• Dissolving ammonium sulphate in water

• Adding calcium carbonate to nitric acid

• Adding potassium hydrogen carbonate to hydrochloric acid

Which statement is correct about exothermic reaction?

• The heat absorbed during bond breaking is more than the heat released during bond formation

• The heat absorbed during bond breaking is less than the heat released during bond formation

• The heat absorbed during bond breaking is equal to the heat released during bond formation

• No heat is absorbed or released during bond breaking and bond formation

The diagram shows the energy profile for the formation of T from R and S.

What is the activation energy for the reaction?

• y kJ mol^-1

• (x + y) kJ mol^-1

• x kJ mol^-1

• (x-y) kJ mol^-1

The reaction between nitrogen and oxygen can be represented by the following equation:

Which of the following energy level diagrams represent the above reaction?

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The following equation shows the reaction between silver nitrate, AgNO₃ and sodium chloride, NaCl.

Which of the following shows that the reaction is an exothermic reaction?

• Silver chloride precipitate is formed in the reaction

• The reaction needs 65.5 kJ of heat energy to form 1 mol of silver chloride

• The total energy absorbed to break the bonds is more than the total energy released during the precipitation of silver chloride.

• The energy contained in silver nitrate and sodium chloride is higher than the energy contained in silver chloride and sodium nitrate.

An experiment was carried out to determine the heat of precipitation for the reaction between silver nitrate and sodium chloride. Table 5 shows the temperature reading of both solutions.

Based on Table 5, which of the following is true?

[Specific heat capacity: 4.0 J g-1 °C^-1; Relative atomic mass: Ag=108; Cl=35.5]

CHOOSE MORE THAN 1 ANSWER!

• 7.2 g white precipitate is formed.

• Heat released during the experiment is 2000 J

• The amount of silver nitrate used is 0.05 mol

• Heat released during the formation of bonds is more than heat absorbed during the breaking of bonds.

In an experiment 2.4 g of magnesium powder is added to 100 cm³ of 2.0 mol dm^-3 copper(II) sulphate solution. The temperature of the mixture increases by 1.0 °C. What is the heat of reaction in the experiment?

[Specific heat capacity of a solution = 4.2 J g^{-1 0}C^-1; Relative atomic mass of Mg=24]

• - 0.42 kJ mol^-1

• - 0.48 kJ mol^-1

• - 4.20 kJ mol-1

• - 4.80 kJ mol^-1

Which of the following acids, when added to 50 cm³ of 0.01 mol dm^-3 sodium hydroxide solution, produce the same rise in temperature of the mixture?

• 50 cm³ of 0.01 mol dm^-3 hydrochloric acid

• 25 cm³ of 0.01 mol dm^-3 sulphuric acid

• 50 cm³ of 0.01 mol dm^-3 nitric acid

• 50 cm³ of 0.01 mol dm^-3 ethanoic acid

When 50 cm³ of 1.0 moldm^-3 nitric acid is mixed with 50 cm³ of 1.0 moldm^-3 sodium hydroxide solution the temperature increases by 6.0 °C. What is the temperature change if the experiment is repeated using 50 cm³ of 2.0 mol dm^-3 nitric acid with 50 cm³ of 1.0 mol dm^-3 sodium hydroxide?

• 3.0 °C

• 6.0 °C

• 9.0 °C

• 12.0 °C

Below are two thermo chemical equations for the neutralization process.

NaOH + HCl -- > NaCl + H2O ; ΔH = -57 kJ mol-1

NaOH + CH₃COOH -- > CH₃COONa + H₂O ; ΔH = -55 kJ mol-1

The value of the heat of neutralization for both processes are different because …..

• the ethanoic acid is less soluble in water.

• the production of sodium ethanoate salt absorbs heat.

• the ethanoic acid produces only a small amount of hydrogen ions.

• greater amount of heat is absorbed to ionize the ethanoic acid molecule.