Calcium oxide and water combine to form calcium hydroxide. This is an example of __________ reaction.
Both combination reaction and exothermic reaction
Understanding the Calcium Oxide and Water Reaction
The reaction between calcium oxide and water is a common chemical process with observable results. Calcium oxide, also known as quicklime, reacts vigorously with water to produce calcium hydroxide, commonly called slaked lime. Let's analyze the type of reaction that occurs.
Chemical Equation for Calcium Oxide and Water Reaction
The balanced chemical equation for this reaction is:
\( \text{CaO(s)} + \text{H}_2\text{O(l)} \rightarrow \text{Ca(OH)}_2\text{(aq)} \)
Here, \( \text{CaO} \) is calcium oxide, \( \text{H}_2\text{O} \) is water, and \( \text{Ca(OH)}_2 \) is calcium hydroxide.
Analyzing the Reaction Type: Combination Reaction
A combination reaction is a type of chemical reaction in which two or more reactants combine to form a single product. Looking at the chemical equation:
- We have two reactants: calcium oxide (\( \text{CaO} \)) and water (\( \text{H}_2\text{O} \)).
- These two reactants combine to form a single product: calcium hydroxide (\( \text{Ca(OH)}_2 \)).
Since two substances are combining to form one new substance, this reaction fits the definition of a combination reaction.
Analyzing the Energy Change: Exothermic Reaction
Chemical reactions can either release energy (exothermic) or absorb energy (endothermic). The reaction between calcium oxide and water is known to produce a significant amount of heat. When quicklime is added to water, the mixture becomes hot, and steam may even be produced due to the heat released. This process is often called the slaking of lime.
An exothermic reaction is a reaction that releases energy in the form of heat or light. Because the reaction of calcium oxide with water releases heat, it is classified as an exothermic reaction.
Evaluating the Options for Calcium Oxide Reaction
Based on our analysis, the reaction between calcium oxide and water is both a combination reaction (two reactants form one product) and an exothermic reaction (heat is released).
- Option 1: Exothermic reaction - This is true, but it doesn't fully describe the reaction.
- Option 2: Combination reaction - This is also true, but it doesn't fully describe the reaction.
- Option 3: Both combination reaction and exothermic reaction - This accurately describes both aspects of the reaction.
- Option 4: Endothermic reaction - This is incorrect, as the reaction releases heat, it does not absorb it.
Therefore, the most accurate description of the reaction between calcium oxide and water is that it is both a combination reaction and an exothermic reaction.
Revision Table: Types of Reactions
| Reaction Type | Description | General Form | Example |
|---|---|---|---|
| Combination | Two or more reactants combine to form a single product. | A + B → AB | \( \text{C} + \text{O}_2 \rightarrow \text{CO}_2 \) |
| Decomposition | A single reactant breaks down into two or more products. | AB → A + B | \( \text{CaCO}_3 \rightarrow \text{CaO} + \text{CO}_2 \) |
| Displacement | One element replaces another in a compound. | A + BC → AC + B | \( \text{Zn} + \text{CuSO}_4 \rightarrow \text{ZnSO}_4 + \text{Cu} \) |
| Double Displacement | Ions are exchanged between two compounds. | AB + CD → AD + CB | \( \text{AgNO}_3 + \text{NaCl} \rightarrow \text{AgCl} + \text{NaNO}_3 \) |
Additional Information: Energy Changes in Chemical Reactions
Chemical reactions involve the breaking and forming of chemical bonds. Energy is required to break bonds, and energy is released when bonds are formed. The overall energy change of a reaction determines whether it is exothermic or endothermic.
- Exothermic Reactions: In these reactions, the energy released during bond formation in the products is greater than the energy required to break bonds in the reactants. The excess energy is released into the surroundings, usually as heat. The temperature of the surroundings increases.
- Endothermic Reactions: In these reactions, the energy required to break bonds in the reactants is greater than the energy released during bond formation in the products. Energy must be absorbed from the surroundings for the reaction to occur. The temperature of the surroundings decreases.
The reaction between calcium oxide and water is a classic example where the energy released is significant, making it noticeably exothermic.
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?
