Defination, example in dynamics equilibrium in chemistry, physics and bio for 9th to 12 class

 

Dynamic Equilibrium

What is Dynamic Equilibrium?

Imagine you are filling a bucket with water while a hole at the bottom lets water leak out. At some point, the water level the same because the water entering is equal to the leaking out. This is what happens in dynamic equilibrium—a process where things continue to change, but overall, nothing appears different.

In chemistry, dynamic equilibrium occurs when the rate of a forward reaction (reactants turning into products) is equal to the rate of the reverse reaction (products turning back into reactants). This means that even though molecules are reacting, their overall amounts remain constant.

Key Points About Dynamic Equilibrium

• In a closed system (no substances can enter or leave).
• The forward and reverse reactions happen at the same speed.
• The amounts of reactants and products stay constant, but molecules are still moving.

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Types of Dynamic Equilibrium

1. Chemical Equilibrium

When a chemical reaction goes in both directions at the same rate.

Example: Making Ammonia (Haber Process)

• Nitrogen gas and hydrogen gas react to form ammonia.
• At equilibrium, ammonia molecules break down into nitrogen and hydrogen at the same rate they form.

Example: Hydrogen Iodide Formation

• Hydrogen gas reacts with iodine gas to make hydrogen iodide.
• At equilibrium, hydrogen iodide splits back into hydrogen and iodine at the same rate.

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2. Phase Equilibrium

 When a substance moves between three states (solid, liquid, gas) at the same rate.

Example: Water Evaporation and Condensation

• In a closed bottle, water evaporates into vapor, but vapor also condenses back into liquid.
• At equilibrium, both happen at the same speed, so the amount of liquid water stays constant.

Example: Ice and Water

• In a freezer at exactly zero degrees Celsius, ice melts into water and water freezes into ice at the same rate.

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3. Solubility Equilibrium

 When a solid dissolves in a liquid at the same rate it crystallizes back into a solid.

Example: Salt in Water

• When you add salt to water, some dissolves, and some settles at the bottom.
• At equilibrium, salt dissolves and re-forms crystals at the same rate, so the total dissolved amount remains unchanged.

Example: Calcium Carbonate in Water

• In a glass of water with chalk powder, some calcium carbonate dissolves while some re-forms as solid.
• At equilibrium, both processes happen at the same speed.

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What Affects Dynamic Equilibrium? (Le Chatelier’s Principle)

A system in equilibrium can be disturbed by changing certain conditions. The system tries to restore balance by shifting in a certain direction.

1. Changing Concentration

• If you add more reactants, the system makes more products.
• If you add more products, the system makes more reactants.

2. Changing Temperature

• If heat is added to a reaction that absorbs heat, it will make more products.
• If heat is added to a reaction that releases heat, it will make more reactants.

3. Changing Pressure (For Gases)

• If pressure increases, the system shifts towards the side with fewer gas molecules.
• If pressure decreases, the system shifts towards the side with more gas molecules.

4. Using a Catalyst

• A catalyst speeds up both forward and reverse reactions equally.
• It does not change the equilibrium position—just makes it reach equilibrium faster.

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How to Represent Dynamic Equilibrium Mathematically

Scientists use numbers to describe how much reactant and product exist at equilibrium.

1. Equilibrium Constant (K)

• If K is large, more products are present.
• If K is small, more reactants are present.

2. Reaction Quotient (Q)

• If Q is less than K, the reaction moves forward.
• If Q is greater than K, the reaction moves backward.
• If Q equals K, the system is at equilibrium.

3. Common Ion Effect

• If a solution already contains an ion from a dissolving salt, the salt will dissolve less.
• Example: Adding table salt to a silver chloride solution makes silver chloride less soluble.

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Where is Dynamic Equilibrium Used in Real Life?

1. Industry (Making Chemicals)

• The Haber process is used to make ammonia for fertilizers.
• The Contact process is used to make sulfuric acid, an important industrial chemical.

2. Biology (Inside Our Bodies)

• The oxygen-carbon dioxide balance in our blood follows equilibrium.
• Enzymes in the body speed up chemical reactions but do not change equilibrium.

3. Medicine and Drugs

• Equilibrium determines how well a drug dissolves in the body.
• Metabolism depends on equilibrium reactions, affecting how fast medicines work.

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Example Problems

Problem 1: Pressure and Equilibrium

In a reaction where gas molecules turn into fewer molecules, what happens if pressure increases?

Answer: The system will shift to produce fewer gas molecules to balance the pressure change.

Problem 2: Temperature and Equilibrium

A reaction absorbs heat when moving forward. What happens if we heat it up?

Answer: More products will be made because the system absorbs the extra heat.

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Conclusion

Dynamic equilibrium is an important concept in chemistry, industry, and biology. It explains how reactions balance over time, and how we can control reactions to get the desired products. Understanding equilibrium helps scientists make fertilizers, develop medicines, and understand how the body works.