CAIE IGCSE Chemistry 5.1 Exothermic and…Reactions

Covered syllabus points

5.1.1—An exothermic reaction transfers 5.1.2—An endothermic reaction takes in 5.1.3—Interpret reaction pathway diagrams 5.1.4—Transfer of thermal energy during a 5.1.5—Activation energy, Ea, as the minimum 5.1.6—And label reaction pathway diagrams 5.1.7—Bond breaking is an endothermic 5.1.8—Enthalpy change of a reaction using

[Maximum number: 1]

Four different fuels are used to heat a beaker of water, for the same amount of time, using the apparatus shown.

Figure for Question 1 — CAIE IGCSE Chemistry

The initial temperature of the water and the temperature after heating by the fuel are recorded.
Which fuel releases the most heat energy?

initial temperature

$/{ }^{\circ} \mathrm{C}$

temperature after

heating $/{ }^{\circ} \mathrm{C}$

[Maximum number: 1]

Which row describes the changes that occur in an endothermic reaction?

energy change

temperature

energy given out to
the surroundings

decreases

energy given out to
the surroundings

increases

energy taken in from
the surroundings

decreases

energy taken in from
the surroundings

increases

[Maximum number: 1]

Which reaction pathway diagram shows the reaction that will give out the most energy?
The scale on the y-axis is the same in each diagram.

Figure for Question 3 — CAIE IGCSE Chemistry

[Maximum number: 1]

Two different experiments are done to find the enthalpy change, $\Delta H$ , of each reaction.
The temperature of each reaction mixture is measured at the beginning of the reaction and after 3 minutes.
experiment 2

experiment 1

Which row gives the correct sign for the value of $\Delta H$ for each experiment and identifies if the reaction is endothermic or exothermic?

experiment 1

experiment 2

negative and endothermic

positive and exothermic

negative and exothermic

positive and endothermic

negative and exothermic

positive and exothermic

negative and endothermic

[Maximum number: 1]

Three statements about activation energy, $E_{a}$ , are listed.

1 Colliding particles must have at least $E_{\mathrm{a}}$ before they can react.
$2 E_{\mathrm{a}}$ for exothermic reactions is always greater than for endothermic reactions.
$3 E_{a}$ is always endothermic.

Which statements are correct?

1, 2 and 3

1 and 2 only

1 and 3 only

2 and 3 only

[Maximum number: 3]

Chemical reactions can involve transfer of thermal energy.

Tetrachloromethane gas, $\mathrm{CCl}_{4}(\mathrm{~g})$ , reacts with steam as shown.

\mathrm{CCl}_{4}(\mathrm{~g})+2 \mathrm{H}_{2} \mathrm{O}(\mathrm{~g}) \rightleftharpoons \mathrm{CO}_{2}(\mathrm{~g})+4 \mathrm{HCl}(\mathrm{~g})

The reaction is reversible. The forward reaction is exothermic.

Fig. 5.1 shows an incomplete reaction pathway diagram for the forward reaction.

\mathrm{CCl}_{4}(\mathrm{~g})+2 \mathrm{H}_{2} \mathrm{O}(\mathrm{~g}) \rightleftharpoons \mathrm{CO}_{2}(\mathrm{~g})+4 \mathrm{HCl}(\mathrm{~g})

Fig. 5.1

On Fig. 5.1:
- insert the formulae of the reactants and products
- draw an arrow, labelled $E_{\mathrm{a}}$ , to show the activation energy
- draw an arrow, labelled $\Delta H$ , to show the transfer of energy in the reaction.

M1 Labels mark

$\mathrm{CCl}_{4}(\mathrm{~g})+2 \mathrm{H}_{2} \mathrm{O}(\mathrm{g})$ on reactant line

AND

$\mathrm{CO}_{2}(\mathrm{~g})+4 \mathrm{HCl}(\mathrm{g})$ on product line

M2 Activation E mark

upward arrow labelled $E_{\mathrm{a}}$ from energy level of reactants to top of 'hump'

M3 Energy change mark

one downward arrow labelled $\Delta \mathrm{H}$

AND

energy change starting from E level of reactants and finishing at E level of products

[Maximum number: 1]

The equation for the reaction between gaseous hydrogen and gaseous iodine to form gaseous hydrogen iodide is shown.

\mathrm{H}_{2}(\mathrm{~g})+\mathrm{I}_{2}(\mathrm{~g}) \rightarrow 2 \mathrm{HI}(\mathrm{~g})

The reaction is exothermic.
Which statement explains why the reaction is exothermic?

Energy is released when H-H and I-I bonds are broken.

The bond energies of the reactants are larger than the bond energies of the products.

The products are at a higher energy level than the reactants.

More energy is released when two HI bonds are formed than is used when the H-H and I-I bonds are broken.

[Maximum number: 1]

The reaction between hydrogen and oxygen releases $486 \mathrm{~kJ} / \mathrm{mol}$ of energy.

2 \mathrm{H}_{2}(\mathrm{~g})+\mathrm{O}_{2}(\mathrm{~g}) \rightarrow 2 \mathrm{H}_{2} \mathrm{O}(\mathrm{~g})

The bond energy of H-H is $436 \mathrm{~kJ} / \mathrm{mol}$ and that of H-O is $464 \mathrm{~kJ} / \mathrm{mol}$ .
What is the bond energy of O=O ?

$430 \mathrm{~kJ} / \mathrm{mol}$

$458 \mathrm{~kJ} / \mathrm{mol}$

$498 \mathrm{~kJ} / \mathrm{mol}$

$984 \mathrm{~kJ} / \mathrm{mol}$

All question bank results loaded

CAIE IGCSE Chemistry 5.1 Exothermic and Endothermic Reactions Topic Practice

Covered syllabus points

Question 1

Question 2

Question 3

Question 4

Question 5

Question 6

Question 7

Question 8