Consider the following reaction: 2HgO \( \stackrel{\Delta}{\longrightarrow} \) 2Hg + O2 The respective state of HgO, Hg and O2 in the above reaction is
Understanding Physical States in Chemical Reactions
The question asks us to identify the physical states of the substances involved in the decomposition of Mercury(II) Oxide (\( \text{HgO} \)) upon heating. The reaction is given as:
\( 2\text{HgO} \stackrel{\Delta}{\longrightarrow} 2\text{Hg} + \text{O}_2 \)
In this reaction, Mercury(II) Oxide (\( \text{HgO} \)) is the reactant, and Mercury (\( \text{Hg} \)) and Oxygen (\( \text{O}_2 \)) are the products. We need to determine their respective states under the reaction conditions, which involve heating (\( \Delta \)).
Physical State of Mercury(II) Oxide (HgO)
Mercury(II) Oxide (\( \text{HgO} \)) is a compound formed from mercury and oxygen. At standard temperature and pressure, \( \text{HgO} \) exists as a solid. It is a reddish-orange or yellow crystalline powder.
The \( \Delta \) symbol above the arrow indicates that the reaction occurs when \( \text{HgO} \) is heated. While heating can cause substances to change state (e.g., melt), Mercury(II) Oxide decomposes into mercury and oxygen at temperatures below its melting point. Therefore, it is typically considered to be in the solid state when the decomposition begins.
- HgO: Solid state
Physical State of Mercury (Hg)
Mercury (\( \text{Hg} \)) is a chemical element, specifically a metal. Mercury is unique among metals because it is a liquid at room temperature and standard atmospheric pressure. This is a well-known property of mercury.
The reaction produces elemental mercury. Even though the reaction involves heating, the product mercury is formed and exists in its stable liquid state at the temperatures typically associated with this decomposition.
- Hg: Liquid state
Physical State of Oxygen (O₂)
Oxygen (\( \text{O}_2 \)) is a diatomic molecule and a chemical element. Oxygen is a gas at standard temperature and pressure.
In the decomposition of \( \text{HgO} \), oxygen is released as a gas. The gaseous state is indicated by \( \text{O}_2 \).
- O₂: Gas state
Summarizing the States
Based on the properties of the substances involved and the reaction conditions, the states are:
- Reactant \( \text{HgO} \): Solid
- Product \( \text{Hg} \): Liquid
- Product \( \text{O}_2 \): Gas
So, the respective states of \( \text{HgO} \), \( \text{Hg} \) and \( \text{O}_2 \) in the reaction are Solid, Liquid, and Gas.
Comparing with Options
Let's compare our findings with the given options:
- Option 1: Liquid, solid, gas (Incorrect - \( \text{HgO} \) is solid, \( \text{Hg} \) is liquid)
- Option 2: Solid, solid, gas (Incorrect - \( \text{Hg} \) is liquid)
- Option 3: Liquid, solid, liquid (Incorrect - \( \text{HgO} \) is solid, \( \text{Hg} \) is liquid, \( \text{O}_2 \) is gas)
- Option 4: Solid, liquid, gas (Correct - Matches our analysis)
Therefore, the correct option is Solid, liquid, gas.
Revision Table: Common Physical States
| Substance Type | Typical State at Room Temp (25°C) & 1 atm | Example |
|---|---|---|
| Ionic Compounds | Solid | NaCl (Sodium Chloride) |
| Most Metals | Solid (except Mercury) | Fe (Iron), Cu (Copper) |
| Mercury (Hg) | Liquid | Hg (Mercury) |
| Non-metal elements (e.g., O₂, N₂, H₂, Cl₂, F₂, Noble Gases) | Gas | O₂ (Oxygen), N₂ (Nitrogen) |
| Some Non-metal elements (e.g., Br₂, I₂) | Liquid (Br₂), Solid (I₂) | Br₂ (Bromine), I₂ (Iodine) |
| Water (H₂O) | Liquid | H₂O (Water) |
Additional Information on Chemical Reactions and States
Chemical equations often include symbols in parentheses after each chemical formula to indicate the physical state of the substance:
- (s) for solid
- (l) for liquid
- (g) for gas
- (aq) for aqueous solution (dissolved in water)
The decomposition of \( \text{HgO} \) could be written more formally as:
\( 2\text{HgO (s)} \stackrel{\Delta}{\longrightarrow} 2\text{Hg (l)} + \text{O}_2 \text{(g)} \)
This notation explicitly shows the states of matter involved in the reaction under the given conditions. Understanding the common states of different types of substances (elements, ionic compounds, molecular compounds) is crucial for interpreting chemical reactions.
Important Questions from Chemical Reaction
- Which one of the following is not an example of a redox reaction?
- Which one of the following is not a pigment?
- Which one of the following reactions is an example of decomposition reaction?
Match List I with List II and select the correct answer using the code given below the Lists:
LIST I
(Chemical process)
LIST II
(Reaction)
A.
Electrolysis of water
1.
Double displacement
reactionB.
Burning of coal
2.
Combination reaction
C.
Iron nail immersed in copper sulphate solution
3.
Decomposition reaction
D.
Addition of barium chloride solution to aluminium sulphate solution
4.
Displacement reaction
Consider the following reaction:
Fe2O3(s) + 2Al(s) → 2Fe(s) + Al2O3(s)
Which of the following statements about the given reaction is NOT correct?
