Calcium hydride reacts with water to form calcium hydroxide and hydrogen gas. This chemical interaction is highly vigorous and exothermic, releasing a significant amount of heat.
Understanding the Reaction: Calcium Hydride and Water
Calcium hydride ($\text{CaH}_2$) is a powerful desiccant, meaning it has a strong affinity for water. When this solid compound comes into contact with liquid water ($\text{H}_2\text{O}$), a rapid and energetic chemical reaction ensues, leading to the formation of two distinct products: calcium hydroxide and hydrogen gas.
The Chemical Equation
The reaction between calcium hydride and water can be precisely represented by the following balanced chemical equation:
$\text{CaH}_2 \text{(s)} + 2\text{H}_2\text{O} \text{(l)} \rightarrow \text{Ca(OH)}_2 \text{(aq)} + 2\text{H}_2 \text{(g)}$
Let's break down what each component signifies:
- $\text{CaH}_2 \text{(s)}$: Represents solid calcium hydride.
- $2\text{H}_2\text{O} \text{(l)}$: Denotes two molecules of liquid water reacting.
- $\text{Ca(OH)}_2 \text{(aq)}$: Indicates calcium hydroxide, which forms an aqueous solution (as it is sparingly soluble in water and often appears as a milky suspension).
- $2\text{H}_2 \text{(g)}$: Shows the production of two molecules of hydrogen gas, released as a gas.
Nature and Characteristics of the Reaction
This reaction is characterized by several important features:
- Vigorous: The reaction proceeds very quickly upon contact, often with noticeable effervescence.
- Exothermic: It releases a considerable amount of heat into the surroundings. This heat generation can be substantial, sometimes even igniting the liberated hydrogen gas, especially if the reaction occurs rapidly in a confined space or with a large quantity of reactants.
- Gas Evolution: The most striking feature is the rapid bubbling, which is the hydrogen gas being released.
Products Formed
As per the reference, the two main products of this reaction are calcium hydroxide and hydrogen gas.
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Calcium Hydroxide ($\text{Ca(OH)}_2$):
- Commonly known as slaked lime.
- It is a white, powdery solid that is sparingly soluble in water, forming a basic (alkaline) solution.
- It finds applications in various industries, including construction (in mortar and plaster), water treatment (to adjust pH), and agriculture (to neutralize acidic soils).
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Hydrogen Gas ($\text{H}_2$):
- A colorless, odorless, and highly flammable gas.
- It is the lightest element and lighter than air.
- Due to its extreme flammability, the generation of hydrogen gas requires careful handling and ventilation during the reaction.
Practical Implications and Safety Considerations
The high reactivity of calcium hydride with water makes it an excellent and widely used drying agent (desiccant) for various substances, including organic solvents, gases, and alcohols, where strict anhydrous conditions are required. It effectively removes even trace amounts of water by chemically converting it into calcium hydroxide and hydrogen gas.
However, this powerful reactivity also introduces significant safety hazards:
- Fire and Explosion Hazard: The rapid production of highly flammable hydrogen gas, coupled with the heat released by the exothermic reaction, presents a substantial risk of fire or explosion, particularly if conducted in an enclosed area or near ignition sources.
- Heat Generation: The considerable heat produced can cause burns or accelerate other dangerous reactions.
- Corrosivity: The resulting calcium hydroxide solution is alkaline and can be corrosive to skin and eyes.
Therefore, any reaction involving calcium hydride and water must be performed in a well-ventilated environment, away from any potential ignition sources, and with the use of appropriate personal protective equipment (PPE).
Key Aspects of Calcium Hydride + Water Reaction
To provide a concise overview, here's a table summarizing the vital aspects of the reaction:
| Aspect | Description |
|---|---|
| Reactant 1 | Calcium Hydride ($\text{CaH}_2$) - A white solid, potent desiccant |
| Reactant 2 | Water ($\text{H}_2\text{O}$) - Liquid |
| Products Formed | Calcium Hydroxide ($\text{Ca(OH)}_2$) and Hydrogen Gas ($\text{H}_2$) |
| Reaction Type | Hydrolysis (reaction with water), Redox Reaction (hydrogen in $\text{H}^-$ oxidizes to $\text{H}_2$) |
| Energy Change | Exothermic (releases significant heat) |
| Vigor/Speed | Very vigorous and rapid upon contact |
| Safety Concerns | High risk of fire/explosion (due to $\text{H}_2$), substantial heat generation, alkalinity/corrosivity of $\text{Ca(OH)}_2$ solution |
| Primary Practical Use | Effective drying agent for organic solvents, gases, and alcohols, due to its strong affinity for water. |
Conclusion
Calcium hydride reacts vigorously with water to produce calcium hydroxide and flammable hydrogen gas. This exothermic reaction is fundamental to calcium hydride's role as an efficient drying agent, yet it critically highlights the necessity of stringent safety measures due to the liberation of hydrogen gas.
