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Cambridge IGCSE chemistry

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Lesson 2, Topic 5
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Past paper questions

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 Nov 2010 Q6 (b)(i) 

(b)

Use the ideas of the Kinetic theory to explain the following:

(i) 

A sealed container contains nitrogen gas. The pressure of a gas is due to the molecules of the gas hitting the walls of the container.

Explain why the pressure inside the container increases when the temperature is increased.

Answer:

Particles have more energy so they move faster because they have more energy

Anawer

 May 2012 Q1 (a) 

(a) (i)

Sate the name of each of the following changes of state

  • H2O(l)  → H2O(g)

  • H2O(g)  → H2O(l)

(ii)

Which of the above changes of state is exothermic ? Explain your choice.

Answer:

(i)

  • Evaporation : H2O(l)  → H2O(g

  • Condensation : H2O(g)  → H2O(l

(ii)

Condensation is exothermic because energy is given out

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 May 2012 Q1 (c) 

(c)

When liquid nitrogen boils the following change occurs 

  N2(l)  →  N2(g

The boiling point of nitrogen is very low even though the bond between the atoms in a nitrogen molecule is very strong. Suggest an explanation

Answer:

Weak intermolecular forces break when a simple molecular substance boils, but strong covalent bonds between nitrogen atoms within nitrogen molecules do not break when liquid nitrogen boils

Anawer

 Nov 2012 Q2 (a), (b), (c), (d) 

The diagram shows a heating curve for a sample of compound X

(a)

Is X a solid, a liquid or a gas at room temperature, 20oC ?

(b)

Write an equation for the equilibrium which exists in region BC

(c)

Name the change of state which occurs in region DE

(d)

Explain how the curve shows that a pure sample of compound X was used

Answer:

(a)

Liquid

(b)

X(s)  ⇌ X(l)

(c)

Boiling

(d)

In region B-C solid melts as it has one specific temperature

Anawer

 Nov 2014 Q2 (a)

Compound X is a colourless liquid at room temperature

A sample of pure X was slowly heated from -50oC, which is below its melting point, to 90oC, which is above its boiling point. Its temperature is measured every minute and the results are represented on the graph

(i) Complete the equation for the equilibrium present in the region BC

X(s)  ⇌ …….

(ii) What is the significance of temperature t oC ?

(iii) What is the physical state of compound X in the region EF ?

(iv) What would be the difference in the region BC if an impure sample of X had been used

Answer:

(i)

X(s)  ⇌ X(l)

(ii)

melting point / freezing point

(iii)

gas

(iv)

line not horizontal

Anawer

 Nov 2016 Q2 (a), (b) 

Matter can exist as solid, liquid or gas. The arrows show some changes of state

(a) Name the changes of state represented on the diagram

A: ………………

B: ………………

C: ………………

(b) Explain why energy has to be supplied to turn a liquid into a gas

Answer:

(a)

A: melting

B: sublimation

C: condensation

(b)

to overcome the attractive forces between molecules

Anawer

 Nov 2016 Q1 (c) 

Name the following changes of state:

(a) Ice turning into water

(b) Solid carbon dioxide turning directly into gaseous carbon dioxide at room temperature

Answer:

(i) Melting

(ii) Sublimation

Anawer

 Nov 2017 Q2 

The graph shows how the temperature of a substance changes as it is cooled over a period of 30 minutes. The substance is a gas at the start

Each letter on the graph may be used once, more than once or not at all.

(a) Which letter, S,T,V,W,X,Y OR Z shows when :

(i) the particles in the substance have the most kinetic energy

(ii) the particles in the substance are furthest apart

(iii) the substance exists ass both a gas and a liquid

(b) Use the graph to estimate the freezing point of the substance

(c) Name the change of state from solid to a gas

Answer 

(a)

(i) S

(ii) S

(iii) V

(b) Any value in the range 130 – 145 °C

(c) Sublimation

Anawer

 Nov 2018 Q1 

Element X can undergo the following physical changes

 

Give the scientific name for each of the numbered physical changes

(i)

1.

2.

3.

4.

(ii) Explain why the changes shown are physical changes

(iii) State one other difference between boiling and evaporation 

 

 

Answer 

(a)

(i) 

  1. Melting

  2. Condensing 

  3. Freezing 

  4. Sublimation

(ii) Because no new substances are made

(iii) Boiling happens at a specific temperature

 

Anawer