The breaking down of food to carbon dioxide and water is a type of -
a. endothermic reaction
b. thermit reaction
c. exothermic reaction
d. reaction without energy change
Answers
Answer:
Endothermic reaction
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Answer:
Types of Reaction
During a chemical reaction, atoms do not disappear from the mixture and appear elsewhere. Nor do they change from one element to atoms of another element. In fact, during chemical reactions, bonds between atoms are broken and re-made to give rise to new substances. Let’s understand how this happens in different types of reactions.Combination Reaction
These are reactions where two or more reactants combine to give rise to a single product. For example, calcium oxide vigorously reacts with water to produce calcium hydroxide, also known as slaked lime. Slaked lime is used to whitewash walls.
CaO(s) + H2O(l) → Ca(OH)2(aq)
(Quicklime) → (Slaked lime)
Let’s look at some other examples of combination reactions –
Formation of water from hydrogen and oxygen.
2H2(g) + O2(g) → 2H2O(l)
Burning of coal.
C(s) + O2(g) → CO2(g)
Exothermic Reaction
These are types of reactions where along with products, heat is also generated. For example, in the above reaction between calcium oxide and water, a large amount of heat gets produced making the reaction mixture warm. Other examples of exothermic reactions are –
Burning of natural gas
CH4(g) + 2O2 (g) → CO2 (g) + 2H2O (g)
Do you know how we get the energy to do our daily activities? The food we consume is broken down into simpler substances during digestion. For example, bread, potatoes rice etc contain carbohydrates which get broken down to its simpler form glucose. During respiration, glucose combines with oxygen in our cells and provides energy. Therefore, respiration is also an exothermic process.
C6H12O6(aq) + 6O2(aq) → 6CO2(aq) + 6H2O(l) + energy
(Glucose)
Another example of an exothermic reaction is the decomposition of vegetable matter to compost.
Decomposition Reaction
In these types of reactions, a single reactant breaks down to give simpler products. For example, when ferrous sulfate crystals are heated, they lose water and the colour of the crystals changes. This is because ferrous sulfate decomposes to ferric oxide, sulfur dioxide, and sulfur trioxide.
types of reactions
Note: When a decomposition reaction is carried out by heating, it is known as thermal decomposition. Other examples of decomposition reactions include –
Thermal decomposition of calcium carbonate to produce calcium oxide and carbon dioxide is very important in many industries. The product calcium oxide, which is also called lime or quicklime, is used to manufacture cement.
types of reactions
Thermal decomposition of lead nitrate to produce lead oxide, nitrogen dioxide, and oxygen. The brown fumes observed when you heat lead nitrate over a flame are that of nitrogen dioxide.
types of reactions
Electrolysis of water i.e. the decomposition of water into hydrogen and oxygen gas when an electric current is passed through water.
2H2O → 2H2 + O2
types of reactions
Source: Wikipedia
Decomposition of silver chloride or silver bromide when exposed to sunlight. Silver chloride decomposes to give silver and chlorine whereas silver bromide gives silver and bromine. These reactions are used in black and white photography.
types of reactions
Note: Decomposition reactions use up energy in the form of light, heat or electricity. Therefore, they are called endothermic reactions since they use up or absorb energy.
Displacement Reaction
In these type of reactions, one element displaces or removes another element from a compound. Let’s understand this reaction using the following experiment as an example.
Experiment
Clean three iron nails by rubbing them with sandpaper.
Mark two test-tubes as (A) and (B) and fill each tube with 10ml of copper sulfate solution.
Dip two iron nails into the tube (B) for 20 minutes carefully using a thread and keep one nail aside for comparison.
After 20 minutes, remove the iron nails from the copper sulfate solution.
Now, note the intensity of the colour of the copper sulfate solution in the two tubes.
Also, note the colour of the iron nails dipped in the solution versus the one kept aside.
Observations
The copper sulfate solution in tube B is much lighter compared to the solution in tube A.
The iron nails dipped in the copper sulfate solution have turned brown compared to the nail kept aside.
Conclusion
The above observations are a result of the following reaction –
Fe(s) + CuSO4(aq) → FeSO4(aq) + Cu(s)
(Copper sulfate) (Iron sulfate)
In the above reaction, iron has displaced or removed copper from the copper sulfate solution. This is a displacement reaction. Some other examples of displacement reactions are –
Zn(s) + CuSO4(aq) → ZnSO4(aq) + Cu(s)
(Copper sulfate) (Zinc sulfate)
Pb(s) + CuCl2(aq) → PbCl2(aq) + Cu(s)
(Copper chloride) (Lead chloride)
Note: Both zinc and lead are more reactive than copper. Therefore, they displace copper in the above reactions.