What Does One Mean by Exothermic Reaction? Give Example. - Science

Short Note

What does one mean by exothermic reaction? Give example.


Solution 1

Reactions in which heat is released along with the formation of products are called exothermic chemical reactions.

Example: \[\ce{C(s) + O2(g) -> CO2(g) + Heat}\]
\[\ce{2H2(g) + O2(g) -> 2H2O(l) + Heat}\]

Solution 2

A reaction in which heat is released is called an exothermic reaction. Burning of fuel is an example of exothermic reaction. When methane is burned, it gives heat along with carbon dioxide and water.

\[\ce{CH4(g) + 2O2(g) -> CO2(g) + 2H2O(l) + Heat}\]

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Taking into consideration the relationship in the first pair, complete the second pair

2H2 + O2 → 2H2O :Combination Reaction :: 2HgO → 2Hg + O2:_________

Rewrite the following statements by selecting the correct options:
\[\ce{CaCO3 ->[\Delta] CaO + CO2 ^}\] is a __________ reaction.

What type of chemical reaction take place when lime-stone is heated?

Two metals X and Y form the salts XSO4 and Y2SO4, respectively. The solution of salt XSO4 is blue in colour whereas that of Y2SO4 is colourless. When barium chloride solution is added to XSO4 solution, then a white precipitate Z is formed alongwith a salt which turns the solution green. And when barium chloride solution is added to Y2SO4 solution, then the same white precipitate  Z is formed alongwith colourless common salt solution.
(a) What could the metals X and Y be?
(b) Write the name and formula of salt XSO4.
(c) Write the name and formula of salt Y2SO4.
(d) What is the name and formula of white precipitate Z?
(e) Write the name and formula of the salt which turns the solution green in the first case.

Classify the following reactions as decomposition, Also balance the equations.

(A) \[\ce{CaCO3(s)->[heat]CaO(s)+CO2(g)}\]

(B) Zn(s) +`"H"_2"SO"_4`  `→`  `"ZnSO"_4` (S) + `"H"_2` (g) 

(C) `"AgNO"_3` (aq)  + NaCI (aq) `→` Ag CI (S) + `"NaNO"_3` 

(D) `"NH"_3` (g) + HCI (g)  `→` `"NH"_4` CI (S)
(E) `"CuSO"_4` (aq)  + `"H"_2"S"` (g)  `→` CuS (S) + `"H"_2"SO"_4` (I)

(F) Zn (S) + `"CuSO"_4` (aq)  `→` `"ZnSO"_4` N  (aq) + Cu  (s) 

(g) \[\ce{Ca(s)O2(g)->[heat]CaO(s)}\]

(H) NaOH + HCI  `→` NaCI + `"H"_2"O"` 

(I) KOH + `"H"_2"SO"_4`  `→` `"K"_2"SO"_4`  + `"H"_2"O"` 

Explain the following types of chemical reactions giving two examples for each of them decomposition reaction .


Tick the most appropriate answer.

Thermal decomposition of a substance is brought about with the help of

  1. reactants
  2. water
  3. wind
  4. heat

Give scientific reason.

When the gas formed on heating limstone is passed through freshly prepared lime water, the lime water turns milky.

Identify the type of following reaction :

Study the following figure and answer questions. 

a) After heating Calcium carbonate, which gas is formed in a test tube?
b) When we pass this gas through limewater what change, did you observe?
c) Write down the chemical reaction showing the product formation after heating the Calcium carbonate.


How can the rate of the chemical reaction, namely, decomposition of hydrogen peroxide be increased?

Rewrite the following statement by selecting the correct option:
________________ is a decomposition reaction.

Classify the following reaction into different type:

\[\ce{2KClO3(s)->[\Delta] 2KCl(aq) + 3O2(g)}\]

Differentiate between direct combination reaction and a decomposition reaction.

Classify the following reaction into – 

  1. Direct combination 
  2. Decomposition
  3. Displacement
  4. Double decomposition

The reaction is – Zinc hydroxide on heating gives zinc oxide and water.

Give a balanced equation for –

A double decomposition neutralization reaction involving an acid and a base

Complete the statement by filling in the blank with the correct word:

Decomposition of silver salts in the presence of sunlight is an example of _________.

Give a balanced equation for the following type of reaction:

A thermal decomposition reaction in which a metallic nitrate decomposes to give – a basic oxide.

Differentiate between the following:

Thermal decomposition and thermal dissociation.

Differentiate between the following:

Electrolytic decomposition and photochemical decomposition.

The chemical reaction in which two or more products are formed from a single reactant is called _______ reaction.

What is electrolysis?

Explain the reaction given in the figure.

Photolysis is a decomposition reaction caused by ______

Electrolysis is type of ______ reaction.

Chemical volcano is an example of ______ type of reaction.

Which among the following statement(s) is (are) true?

Exposure of silver chloride to sunlight for a long duration turns grey due to

(i) the formation of silver by decomposition of silver chloride.

(ii) sublimation of silver chloride.

(iii) decomposition of chlorine gas from silver chloride.

(iv) oxidation of silver chloride.

When SO2 gas is passed through a saturated solution of H2S, which of the following reaction occurs?

Assertion: Decomposition of vegetable matter into compost is an endothermic reaction.

Reason: Decomposition reaction involves breakdown of a single reactant into simpler products.

Balance the following chemical equation and identify the type of chemical reaction.

`"HgO"("s") overset("(heat)")(->) "Hg"("l") + "O"_2("g")`

On heating blue coloured powder of copper (II) nitrate, in a boiling tube, copper oxide (black), oxygen gas and a brown gas X is formed

  1. Write a balanced chemical equation of the reaction.
  2. Identify the brown gas X evolved.
  3.  Identify the type of reaction.
  4. What could be the pH range of aqueous solution of the gas X?

The reaction of calcium carbonate, with freshly prepared lime water, is shown below:

Answer the questions with the help of a diagram:

  1. What type of reaction does calcium carbonate undergoes?
  2. What change in colour is observed in lime?
  3. Write the chemical equation.

Complete the following reaction:

\[\ce{C_12H_22O11->[Heat]}\] ______ + ______.

What is observed when silver chloride is exposed to sunlight? Give the type of reaction involved.

Write the molecular formula of calcium carbonate.

Write one equation for decomposition reactions where energy is supplied in the form of electricity.


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