Thermochemistry form 5

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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• 
• 
• 

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 2100 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.

When 100 cm³ of 1.0 mol dm^-3 of sodium hydroxide is added to 100 cm³ of 1.0 mol dm^-3 of hydrochloric acid, temperature rises by 7 °C. Which of the following mixtures will produce an increment of 14 °C in temperature?

• 50 cm³ of 1.0 mol dm^-3 of sodium hydroxide 50 cm³ of 1.0 mol dm^-3 of hydrochloric acid

• 50 cm³ of 2.0 mol dm^-3 of sodium hydroxide and 50 cm³ of 2.0 mol dm^-3 of hydrochloric acid

• 100 cm³ of 1.0 mol dm^-3 of sodium hydroxide and 100 cm³ of 4.0 mol dm^-3 hydrochloric acid

• 200 cm³ of 1.0 mol dm^-3 sodium hydroxide and 200 cm³ of 1.0 mol dm^-3 hydrochloric acid

The following thermochemical equation shows a combustion reaction between hexane. C₆H₁₄ and oxygen.

What is the mass of hexane need to be burnt to produce heat that can heat up 2 kg of water from 25 °C to 100°C?

[Relative atomic mass : C=12, H=l; specific heat capacity of water = 4.2 Jg^{-1 °}C^-1]

• 5.16 g

• 5.56 g

• 15.48 g

• 16.67 g