Chapter No: 05
Physical and Chemical Changes of Matter
Q1: Differentiate between physical and chemical changes?
Ans: Physical changes are reversible while chemical changes are irreversible.
Physical changes refer to alterations in the physical properties of a substance without any changes occurring at the molecular level. These changes are typically reversible, meaning the substance can return to its original state. Examples of physical changes include changes in shape, size, state of matter (such as melting, freezing, or boiling), and dissolving. In contrast, chemical changes involve a transformation at the molecular level, resulting in the formation of new substances with different chemical properties. Chemical changes are usually irreversible and involve the breaking and forming of chemical bonds. Examples of chemical changes include combustion, rusting, digestion, and the fermentation of food.
Q2: What changes occur in the state of water when it freezes, boils, condenses and melts?
Ans: Melting: Water changes from solid into liquid. Freezing: Water changes from liquid into solid.
Boiling: Water changes from liquid into vapors.
Condensation: Water changes from vapors into liquid.
When water undergoes freezing, it changes from a liquid state to a solid state. The molecules in water slow down and arrange themselves in a regular pattern, forming a crystal lattice structure. This process releases heat energy, causing the temperature of the water to decrease.
Boiling refers to the transition of water from a liquid state to a gaseous state. When water reaches its boiling point (which is 100 degrees Celsius or 212 degrees Fahrenheit at sea level), the heat energy causes the water molecules to gain enough kinetic energy to overcome the intermolecular forces holding them together. The molecules become more energetic, break free from the liquid phase, and form water vapor or steam.
Condensation is the opposite of boiling and occurs when water vapor or steam cools down. As the temperature decreases, the water vapor molecules lose kinetic energy and slow down. They come closer together, forming clusters or liquid droplets. This transition changes the state of water from a gaseous form to a liquid form.
Melting refers to the process of transitioning water from a solid state (ice) to a liquid state. When heat is applied to ice, the energy is absorbed by the molecules, causing them to gain kinetic energy and vibrate more rapidly. As a result, the intermolecular forces holding the ice lattice together weaken, and the solid structure breaks down, transforming the ice into liquid water.
In summary, freezing converts water from a liquid to a solid, boiling converts it from a liquid to a gas, condensation converts it from a gas to a liquid, and melting converts it from a solid to a liquid.
Q3: Enlist the factors affection the dissolution of materials into water?
Ans:
1. By increasing temperature
2. By stirring
3. By breaking the solids in smaller pieces the dissolution of materials into water can be influenced by several factors. Here are some of the key factors that affect the dissolution process:
1. Temperature: Generally, an increase in temperature enhances the rate of dissolution. Higher temperatures provide more kinetic energy to the particles, leading to increased collisions and a greater chance of breaking the intermolecular forces holding the solute particles together
2. Surface Area: The surface area of the solute that comes into contact with the solvent affects the rate of dissolution. A greater surface area provides more opportunities for solvent molecules to interact with the solute particles, accelerating the dissolution process. Finely powdered or crushed solute dissolves faster than larger chunks or solid piece
3. Agitation or Stirring: Stirring or agitation promotes the mixing of solvent and solute, allowing fresh solvent molecules to come into contact with the solute. This facilitates the dissolution process by maintaining a concentration gradient and speeding up the interaction between solute and solvent particle
4. Concentration: The concentration of the solute in the solvent affects the dissolution rate. Generally, a higher concentration gradient between the solute and solvent leads to a faster dissolution process. However, there is a limit to how much solute can dissolve in a given amount of solvent, known as solubility
5. Nature of the Solute and Solvent: The nature of the solute and solvent plays a significant role in dissolution. Polar solvents (e.g., water) tend to dissolve polar solutes, while no polar solvents dissolve no polar solutes. The compatibility of intermolecular forces between solute and solvent determines the dissolution process
6. Pressure (for Gases): In the case of gas solutes, an increase in pressure can enhance their solubility in a solvent. This is known as Henry's Law, which states that the solubility of a gas is directly proportional to its partial pressure above the solvent
These factors collectively influence the dissolution of materials into water or any other solvent, affecting the rate and extent of the dissolution process.t.s.y.s.s.r.
Q4: Define the following: Condensation, Evaporation, Physical change, Chemical change.
Q5: Differentiate between dilute and concentrated solution?
Ans: Dilute solution: It has small amount of solute.
Concentrated solution: It has a high amount of solute.
Dilute and concentrated solutions are terms used to describe the relative amount of solute dissolved in a solvent. Here's how they differ:
Dilute solution:
A dilute solution has a relatively small amount of solute dissolved in a larger amount of solvent. In other words, the concentration of the solute in the solution is low. Dilute solutions often appear less saturated and have a lighter color or weaker taste compared to concentrated solutions. The ratio of solute to solvent is lower in a dilute solution.
Concentrated solution:
A concentrated solution, on the other hand, has a relatively large amount of solute dissolved in a smaller amount of solvent. The concentration of the solute in the solution is high. Concentrated solutions often appear more saturated and have a darker color or stronger taste compared to dilute solutions. The ratio of solute to solvent is higher in a concentrated solution.
The terms "dilute" and "concentrated" are relative and depend on the specific context or application. For example, a solution considered dilute in one situation may be considered concentrated in another. It is important to note that concentration can be expressed in various units, such as molarity, mass/volume percent, or parts per million, depending on the nature of the solute and solvent.
Q6: Enlist three identification features of chemical changes?
Ans: 1. Decay 2. Burning 3.Rusting
When observing a system or substance, there are several identification features that can indicate the occurrence of a chemical change. Here are three common features to look for:
1. Formation of new substances: Chemical changes involve the transformation of one or more substances into different substances with distinct chemical properties. Look for signs of new products being formed, such as the appearance of gas bubbles, a color change, the formation of a precipitate (a solid that separates from a solution), or the generation of heat or light. These observations suggest that chemical reactions have taken place, indicating a chemical change.
2. Irreversibility: Chemical changes are typically irreversible. Once a chemical reaction occurs, it is challenging or impossible to revert the substances back to their original form. If the change is permanent and cannot be easily undone by physical means, it is likely a chemical change.
3. Energy changes: Chemical reactions often involve energy exchanges. Pay attention to any noticeable changes in energy, such as the release or absorption of heat or light. If the reaction generates or absorbs a significant amount of energy, it indicates that a chemical change is taking place.
It's important to consider these identification features collectively and not rely on a single observation. Additionally, the context and specific conditions of the system being observed should be taken into account to make accurate determinations about the occurrence of a chemical change.
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