5.1 Energetics

Question 1

Marks: 1

In a calorimetric experiment 2.50 g of a fuel is burnt in oxygen. 30 % of the energy released during the combustion is absorbed by 500 g of water, the temperature of which rises from 25 °C to 68 °C.

The specific heat capacity of water is 4.2 J g^–1 K^–1.

What is the total energy released per gram of fuel burnt?

$\frac{500 \times 4.2 \times (68 - 25)}{2.5}$
$\frac{500 \times 4.2 \times (273 + (68 - 25)) \times 100}{30 \times 2.5}$
$\frac{500 \times 4.2 \times (68 - 25) \times 100}{30 \times 2.5}$
$\frac{500 \times 4.2 \times (68 - 25) \times 100}{30}$

Question 2

Marks: 1

The reaction of hydrochloric acid with sodium hydroxide produced an overall temperature increase of 24.4 K.

Given the following data, how much thermal energy was evolved during this reaction?

Initial temperature of 25.0 cm³ hydrochloric acid = 17.6 ^oC

Initial temperature of 25.0 cm³ sodium hydroxide = 18.5 ^oC

The specific heat capacity of water is 4.18 J g^-1 K^-1.

(25.0 x 4.18 x 6.8) + (25.0 x 4.18 x 5.9)
$\frac{(25.0 \times 4.18 \times 6.8) + (25.0 \times 4.18 \times 5.9)}{2}$
50.0 x 4.18 x $(\frac{6.8 + 5.9}{2})$
(50.0 x 4.18 x 6.8) + (50.0 x 4.18 x 5.9)

Question 3

Marks: 1

The temperature rise when 0.1 MJ of heat energy is absorbed by 2.5 kg of solid aluminium is 44.4 ^oC.

What is the specific heat capacity of aluminium, in J g^-1 K^-1?

$\frac{100000}{2.5 \times 44.4}$
$\frac{100000}{2500 \times 44.4}$
$\frac{0.1}{2.5 \times 44.4}$
$\frac{0.1}{2500 \times 44.4}$

Question 4

Marks: 1

An iron cube, with a mass of 0.5 kg, increases in temperature by 12.7 K when heated.

The specific heat capacity of iron is 0.448 J K^-1 g^-1.

What is the enthalpy change, in kJ mol^-1, for heating the iron cube?

0.448 x 12.7 x 55.85
$\frac{0.448 \times 12.7 \times 500^{2}}{1000 \times 55.85}$
$\frac{0.448 \times 12.7 \times 55.85}{1000}$
$- \frac{0.448 \times 12.7 \times 55.85}{1000}$

Question 5

Marks: 1

When completing experiments to measure enthalpy change for exothermic processes, which of the following is not a reason for the experimental data to be lower than the expected value?

Heat loss through convection
Water vapour released as a product
An inadequate supply of oxygen during combustion
Heat transfer to the system

Question 6

Marks: 1

Heptathiepane, S₇, can undergo complete combustion to form sulfur dioxide.

S₇ (s) + 7O₂ (g) → 7SO₂ (g)

Which enthalpy changes can be used to describe this reaction?

	ΔH_f^θ	ΔH_c^θ	ΔH_r
A	✔	x	✔
B	x	✔	✔
C	x	✔	x
D	x	x	✔

Question 7

Marks: 1

A student obtained the following experimental results for the enthalpy of combustion of cyclohexane (C₆H₁₂).

Mass of water / g	50.00
Initial temperature of the water / °C	19.60
Initial mass of spirit burner and cyclohexane / g	186.79
Final mass of spirit burner and cyclohexane / g	186.29

The student determined from this experiment that the enthalpy of combustion of cyclohexane is –1216 kJ mol^–1

The specific heat capacity of water = 4.18 J g^–1 K^–1The relative molecular mass (M_r) of cyclohexane = 84.18

Which calculation will correctly determine the final temperature of the water in this experiment?

19.60 + $\frac{608}{50.00 \times 4.18 \times 84.18}$
19.60 + $\frac{60800}{5.00 \times 4.18 \times 84.18}$
19.60 + $\frac{1216 \times 84.18}{25.00 \times 4.18}$
19.60 + $\frac{1216000 \times 84.18}{25.00 \times 4.18}$

Question 8

Marks: 1

The diagrams below show a simple calorimeter that is commonly used in the school laboratory and the more accurate chamber calorimeter. q8_5-1_ib_sl_hard_mcq

Simple calorimeter

Chamber calorimeter

Which of the following statements correctly explain why the chamber calorimeter is more accurate?

There is less heat loss
There is more complete combustion
There is less fuel lost

I and II only
I and III only
II and III only
I, II and III

Question 9

Marks: 1

Which of the following assumptions are correct when completing the calorimetry experiment and subsequent calculations for the neutralisation of 25.0 cm³ sulfuric acid by 25.0 cm³ barium hydroxide?

That both solutions have the same initial temperature
The value of m in q = mcΔT is 50 g
Heat is lost to the surroundings

I and II only
I and III only
II and III only
I, II and III

Question 10

Marks: 1

The heat produced by the combustion of magnesium is used to heat some water.

Which values are needed to calculate the energy transferred during the reaction?

The mass of magnesium
The mass of the water
The temperature change of the water

I and II only
I and III only
II and III only
I, II and III

DP IB Chemistry: HL

Topic Questions

5.1 Energetics

Question 1

Question 2

Question 3

Question 4

Question 5

Question 6

Question 7

Question 8

Question 9

Question 10

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