ChemistryICSE Class 8 · Chemical Reactions

Neutralisation, Exothermic and Endothermic Changes, and Classification of Oxides (ICSE Class 8)

Updated 17 October 2026 · Fact-checked

Neutralisation is acid + base → salt + water, an exothermic double displacement. Exothermic changes give out heat; endothermic changes take it in (dissolving ammonium chloride). Heating carbonates and nitrates gives oxides, which are basic, acidic, amphoteric or neutral.

Notice the arrows: heat leaves an exothermic change like neutralisation, and enters an endothermic one like dissolving ammonium chloride.

Illustration drawn for QuestionBuddy.

Understand Neutralisation, Exothermic and Endothermic Changes, and Oxides

Neutralisation. An acid reacts with a base to form a salt and water:

$N a O H + H C l \to N a C l + H_{2} O$

It is a double displacement reaction and is exothermic. Uses: antacid tablets for acidity, lime on acidic soil, baking soda on an ant bite.

Exothermic and endothermic changes.

Exothermic: heat is given out; surroundings become warmer. Examples: burning fuels, respiration, neutralisation, quicklime with water ( $C a O + H_{2} O \to C a (O H)_{2}$ ).
Endothermic: heat is taken in; surroundings become cooler. Examples: dissolving ammonium chloride in water (the beaker feels cold), photosynthesis, heating calcium carbonate.

Touch test: warmer outside of the tube means exothermic, colder means endothermic.

Making oxides.

Heating carbonates: $C a C O_{3} \to C a O + C O_{2}$ ; $P b C O_{3} \to P b O + C O_{2}$ .
Heating nitrates: $2 P b (N O_{3})_{2} \to 2 P b O + 4 N O_{2} + O_{2}$ (brown nitrogen dioxide).
Heating an element in air: $2 M g + O_{2} \to 2 M g O$ ; $S + O_{2} \to S O_{2}$ ; $C + O_{2} \to C O_{2}$ .

Classifying oxides.

Type	Usually from	Behaviour	Examples
Basic	metals	react with acids to give salt + water	CaO, MgO, Na₂O, CuO
Acidic	non-metals	react with bases to give salt + water	CO₂, SO₂, SO₃
Amphoteric	some metals	react with both acids and bases	ZnO, PbO, Al₂O₃
Neutral	some non-metals	neither	CO, H₂O, N₂O, NO

$Z n O + 2 H C l \to Z n C l_{2} + H_{2} O$ and $Z n O + 2 N a O H \to N a_{2} Z n O_{2} + H_{2} O$ .

Neutralisation, Exothermic and Endothermic Changes, and Oxides: formulas and key facts

Neutralisation: $acid + base \to salt + water$; Exothermic.
Heating carbonate or nitrate: $C a C O_{3} \to C a O + C O_{2} 2 P b (N O_{3})_{2} \to 2 P b O + 4 N O_{2} + O_{2}$; Metal oxide formed.
Amphoteric oxide: $Z n O + 2 H C l \to Z n C l_{2} + H_{2} O Z n O + 2 N a O H \to N a_{2} Z n O_{2} + H_{2} O$; Reacts with acid and base.
Heat changes: Exothermic: heat out, warmer | Endothermic: heat in, colder; Test: touch the tube.

How to solve Neutralisation, Exothermic and Endothermic Changes, and Oxides questions

Use the behaviour with acids and bases to classify an oxide, and the temperature change for energy questions.

1Metal oxide: usually basic; non-metal oxide: usually acidic; check the exceptions.
2Reacts with both acid and alkali: amphoteric.
3Neither: neutral (CO, H₂O, NO).
4Cooler after mixing: endothermic; warmer: exothermic.
5Count atoms to balance, e.g. 2Pb(NO₃)₂: Pb 2, N 4, O 12.

Neutralisation, Exothermic and Endothermic Changes, and Oxides in real life

Each concept, met in an everyday situation. Read the situation, try the problem, then check the solution. The one-line hook is what to remember.

Antacid for acidity

Suppose a person has acidity after a heavy meal and takes an antacid tablet containing a base.

Why does the discomfort ease?

Try it first, then show the solutionSolution

The excess acid in the stomach reacts with the base.
Neutralisation gives a salt and water, so the acidity falls.

Answer: Neutralisation of the extra stomach acid by the base.

Memory hook: Base cancels acid.

A cold pack

Imagine ammonium chloride is stirred into water in a beaker and the beaker feels cold.

Classify the change.

Try it first, then show the solutionSolution

The surroundings lose heat to the dissolving solid.
Heat is taken in: the change is endothermic.

Answer: Endothermic.

Memory hook: Cold to touch, endothermic.

Tricks to remember Neutralisation, Exothermic and Endothermic Changes, and Oxides

Short memory aids. Say each one aloud once, then use it on a question the same day.

Exo = exit
Exothermic: heat exits. Endo = enters.
Use it when: Heat changes.
Metals basic, non-metals acidic
Oxides of metals are mostly basic, of non-metals mostly acidic; ZnO, Al₂O₃, PbO are amphoteric.
Use it when: Oxides.
CO, H₂O, NO neutral
The neutral oxides to remember.
Use it when: Exceptions.

Neutralisation, Exothermic and Endothermic Changes, and Oxides: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

Example 1: Amphoteric oxide · 1 mark · MCQBoard level

Which oxide reacts with both hydrochloric acid and sodium hydroxide?
(a) CaO
(b) CO₂
(c) ZnO
(d) CO

Try it first, then show the solutionSolution

ZnO is amphoteric: it gives ZnCl₂ with acid and Na₂ZnO₂ with alkali.

Answer: (c) ZnO

Example 2: Neutralisation · 2 marks · Short answerBoard level

Define neutralisation, write an equation and give one use.

Try it first, then show the solutionSolution

An acid reacts with a base to form a salt and water. (1)
$N a O H + H C l \to N a C l + H_{2} O$ ; use: antacid (or lime on acidic soil). (1)

Answer: Acid + base → salt + water

Example 3: Sort the oxides · 3 marks · Short answerHarder board level

Classify as basic, acidic, amphoteric or neutral: CaO, CO₂, Al₂O₃, CO, SO₂, MgO, ZnO, H₂O.

Try it first, then show the solutionSolution

Basic: CaO, MgO. (¾)
Acidic: CO₂, SO₂. (¾)
Amphoteric: Al₂O₃, ZnO. (¾)
Neutral: CO, H₂O. (¾)

Answer: Basic CaO, MgO; acidic CO₂, SO₂; amphoteric Al₂O₃, ZnO; neutral CO, H₂O

Example 4: Heating salts · 3 marks · Short answerHarder board level

Write balanced equations for heating (a) limestone, (b) lead(II) nitrate. State the gases formed, including any colour. Show the atom count for (b).

Try it first, then show the solutionSolution

(a) $C a C O_{3} \to C a O + C O_{2}$ (colourless CO₂). (1)
(b) $2 P b (N O_{3})_{2} \to 2 P b O + 4 N O_{2} + O_{2}$ (brown NO₂ and oxygen). (1)
Atoms: Pb 2 = 2; N 4 = 4; O $12 = 2 + 8 + 2$ . (1)

Answer: (a) CaO + CO₂ (b) PbO + 4NO₂ + O₂

Example 5: Hot and cold · 4 marks · Case-basedHOTS / competency

In two beakers: (A) solid ammonium chloride is dissolved in water; (B) quicklime is added to water. (a) What do you feel in each? (b) Classify each change. (c) Write the equation for B. (d) Is A a chemical reaction? Give a reason.

Try it first, then show the solutionSolution

(a) A feels cold; B feels hot. (1)
(b) A is endothermic; B is exothermic. (1)
(c) $C a O + H_{2} O \to C a (O H)_{2}$ . (1)
(d) It is dissolving, a physical process in which the solid can be recovered by evaporation, though it takes in heat. (1)

Answer: (a) cold, hot (b) endo, exo (c) CaO + H₂O → Ca(OH)₂

Where students lose marks in Neutralisation, Exothermic and Endothermic Changes, and Oxides

The slips examiners see most often, and what to write instead.

Mistake: Saying all metal oxides are basic
ZnO, Al₂O₃ and PbO are amphoteric.
Wrong working
"ZnO is a basic oxide."
Right working
"ZnO is amphoteric."
Do this: Learn the three amphoteric oxides.
Mistake: Mixing up exo and endo
Exothermic gives out heat.
Wrong working
"Dissolving ammonium chloride is exothermic."
Right working
"It is endothermic: the beaker gets cold."
Do this: Use the touch test.
Mistake: Unbalanced decomposition of nitrate
Oxygen count must match.
Wrong working
$P b (N O_{3})_{2} \to P b O + N O_{2} + O_{2}$ .
Right working
$2 P b (N O_{3})_{2} \to 2 P b O + 4 N O_{2} + O_{2}$ .
Do this: Count O last.

Exam tips

Define neutralisation with salt and water.
Use the touch test and surroundings to classify energy changes.
Learn the table of oxides with two examples each.
Balance after writing correct formulae.

Practice questions on Neutralisation, Exothermic and Endothermic Changes, and Oxides

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

Q1 · 1 mark · Very short answerBoard level
Give one example of an exothermic change.
Hint
Gives out heat.
Answer
Burning of fuel (or neutralisation, quicklime with water).
Q2 · 3 marks · Short answerHarder board level
Zinc oxide reacts with both acids and alkalis. Write the two equations and name this property.
Hint
Amphoteric.
Answer
$Z n O + 2 H C l \to Z n C l_{2} + H_{2} O$ and $Z n O + 2 N a O H \to N a_{2} Z n O_{2} + H_{2} O$ ; the property is amphoteric nature.
Q3 · 2 marks · Short answerHarder board level
Why is lime (calcium oxide or hydroxide) added to acidic soil? Write the equation for calcium hydroxide with hydrochloric acid.
Hint
Base meets acid.
Answer
The base neutralises the acid in the soil. $C a (O H)_{2} + 2 H C l \to C a C l_{2} + 2 H_{2} O$ .
Q4 · 3 marks · Short answerHarder board level
Count the atoms on each side of $2 P b (N O_{3})_{2} \to 2 P b O + 4 N O_{2} + O_{2}$ and show it is balanced. What is the colour of the gas that fumes?
Hint
Brackets multiply.
Answer
Left: Pb 2, N 4, O 12. Right: Pb 2, N 4, O $2 + 8 + 2 = 12$ . Balanced. The gas NO₂ is brown.
Q5 · 4 marks · Long answerHOTS / competency
Four oxides are tested: P turns red litmus blue and reacts with acids; Q turns blue litmus red; R has no effect on litmus; S reacts with both acids and alkalis. Classify P, Q, R and S, giving one example each.
Hint
Use the table.
Answer
P: basic (e.g. MgO). Q: acidic (e.g. SO₂). R: neutral (e.g. CO). S: amphoteric (e.g. ZnO).

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1.Products of neutralisation?Show answer
Salt and water.
2.CO is what kind of oxide?Show answer
Neutral.
3.ZnO is?Show answer
Amphoteric.
4.Dissolving NH₄Cl is?Show answer
Endothermic.
5.Colour of NO₂?Show answer
Brown.

Neutralisation, Exothermic and Endothermic Changes, and Oxides: frequently asked questions

What is neutralisation?

It is the reaction of an acid with a base to form a salt and water; it gives out heat (exothermic).

What is the difference between exothermic and endothermic changes?

Exothermic changes give out heat and warm the surroundings; endothermic changes take in heat and cool the surroundings.

What are amphoteric oxides?

Oxides that react with both acids and bases to give salt and water, such as ZnO, Al₂O₃ and PbO.