What is Charles Law? Definition, Formula & Application Explained
Charles Law is essential in chemistry and helps students understand various practical and theoretical applications related to this topic. Knowing Charles Law makes it easier to solve numerical problems about gases, visualize gas behavior in real life, and connect theory to experiments for scoring well in competitive exams and school tests.
What is Charles Law in Chemistry?
A Charles Law refers to the principle that, for a fixed mass of gas at constant pressure, the volume is directly proportional to its absolute temperature (in Kelvin). This concept appears in chapters related to states of matter, thermodynamics, and gas laws, making it a foundational part of your chemistry syllabus.
Molecular Formula and Composition
The molecular formula related to Charles Law is expressed as V/T = k, or more specifically, V1/T1 = V2/T2. It consists of variables—V (volume in liters) and T (absolute temperature in Kelvin)—and is categorized under gas behavior relationships in physical chemistry.
Preparation and Synthesis Methods
Since Charles Law is a gas law (not a chemical compound), it is verified using controlled experiments in the laboratory. Typical methods include heating or cooling a fixed mass of gas inside a sealed cylinder with a movable piston while keeping the pressure constant. The changes in gas volume are measured as the temperature is systematically changed, demonstrating the law in real time.
Physical Properties of Charles Law
Charles Law is not a substance, but it describes important physical properties and relationships:
- Volume: Changes proportionally with temperature (in Kelvin).
- Temperature: Must use absolute (Kelvin) scale for correct outcomes.
- Pressure: Must remain constant for Charles Law to hold true.
- Graph: Produces a straight line when volume vs temperature (in K) is plotted.
Chemical Properties and Reactions
As Charles Law is a relationship, not a chemical, it doesn't exhibit chemical reactions directly. However, it supports understanding of:
- Gas expansion upon heating at constant pressure
- Decrease in volume upon cooling
- Foundation for predicting changes in gases during chemical processes
Frequent Related Errors
- Using Celsius instead of Kelvin in Charles Law equations
- Confusing volume-temperature (Charles Law) with pressure-volume (Boyle’s Law)
- Assuming pressure can change—Charles Law applies only when pressure is constant
- Failing to convert all temperature values to the Kelvin scale
Uses of Charles Law in Real Life
Charles Law is widely used to explain:
- Shrinking of a balloon in a cold fridge and expansion when heated up
- Lung capacity variations in cold and warm environments
- Hot air balloon flight—heated air expands to lift the balloon
- Car tire pressure changes with seasonal temperature changes
Relevance in Competitive Exams
Students preparing for NEET, JEE, and Olympiads should be familiar with Charles Law, as it often features in concept-based and application-based questions in the gas laws and thermodynamics chapters. All major boards like CBSE and state boards include Charles Law numericals in both objective and subjective formats.
Relation with Other Chemistry Concepts
Charles Law is closely related to topics such as Boyle’s Law (pressure-volume relationship) and Gay-Lussac’s Law (pressure-temperature relationship), helping students build a conceptual bridge between various chapters. It also forms the basis for the Ideal Gas Law and Combined Gas Law.
Step-by-Step Reaction Example
Suppose a balloon has a volume of 2.00 L at 300 K. What will its volume be at 360 K, keeping pressure constant?
1. Write Charles Law: V1/T1 = V2/T22. Substitute values: 2.00/300 = V2/360
3. Cross-multiplied: V2 = (2.00 × 360)/300 = 2.40 L
4. Final Answer: At 360 K, the balloon’s volume becomes 2.40 L
Lab or Experimental Tips
Remember Charles Law by the “Kelvin Rule”—always use temperature in Kelvin, never Celsius! Vedantu educators often use the balloon-in-fridge experiment to visually demonstrate this—keep a balloon in the freezer and watch it shrink due to volume contracting at lower temperatures.
Try This Yourself
- What happens if you plot gas volume vs Celsius temperature? How does the graph change if you use Kelvin?
- Find the new volume of a 3.00 L syringe at 273 K when temperature is increased to 546 K, keeping pressure constant.
- Write the statement and formula of Charles Law from memory. Check it with classroom notes.
Final Wrap-Up
We explored Charles Law—its relationship, experimental significance, problem-solving approach, and real-life relevance. For more in-depth explanations, sample problems, and exam-prep tricks, explore live classes, notes, and expert sessions only on Vedantu.
Boyle’s Law | Gay-Lussac’s Law | Combined Gas Law | Ideal Gas Law | States of Matter
FAQs on Charles Law – Statement, Explanation, Formula, Graph & Examples
1. What is Charles's Law in chemistry?
Charles's Law, also known as the law of volumes, describes the relationship between the volume and temperature of a fixed mass of gas at constant pressure. It states that the volume of a gas is directly proportional to its absolute temperature (in Kelvin) when pressure is held constant. This means that as temperature increases, volume increases proportionally, and vice versa.
2. How do you write the mathematical formula for Charles's Law?
The mathematical formula for Charles's Law is: V₁/T₁ = V₂/T₂, where V₁ and V₂ represent the initial and final volumes, and T₁ and T₂ represent the initial and final absolute temperatures (in Kelvin).
3. What is the graphical representation of Charles's Law?
A graph of Charles's Law plots volume (V) on the y-axis and absolute temperature (T) on the x-axis. It results in a straight line passing through the origin, demonstrating the direct proportionality between volume and temperature. Extrapolating this line to zero volume suggests a theoretical temperature of absolute zero.
4. Can you give a real-life example of Charles's Law?
A hot air balloon is a classic example. Heating the air inside the balloon increases its volume, making it less dense than the surrounding air and causing it to rise. Conversely, cooling the air reduces its volume, causing the balloon to descend. Another example is a balloon shrinking in cold weather or expanding in warm weather.
5. How is Charles's Law derived or proven?
Charles's Law can be derived from the ideal gas law (PV = nRT) by holding pressure (P) and the number of moles (n) constant. This simplifies the equation to V/T = constant (k), which directly leads to the Charles's Law formula. Experimental observations of gas expansion with temperature consistently support the law.
6. Why must temperature be in Kelvin for Charles's Law equations?
Temperature must be in Kelvin because Charles's Law describes a direct proportionality between volume and temperature. The Kelvin scale is an absolute temperature scale, meaning it starts at absolute zero (0 K), where theoretically, the volume of an ideal gas would be zero. Using Celsius or Fahrenheit would introduce a non-zero intercept, breaking the direct proportionality.
7. How does Charles's Law fit into the Combined Gas Law?
Charles's Law is a component of the Combined Gas Law, which combines Boyle's Law, Charles's Law, and Gay-Lussac's Law. The Combined Gas Law expresses the relationship between pressure, volume, and temperature of a fixed amount of gas: P₁V₁/T₁ = P₂V₂/T₂. If pressure is held constant (P₁=P₂), the Combined Gas Law reduces to Charles's Law.
8. What are the limitations of Charles's Law in practical scenarios?
Charles's Law applies perfectly only to ideal gases. Real gases deviate from ideal behavior at high pressures and low temperatures, where intermolecular forces become significant. At very low temperatures, gases may even condense into liquids, invalidating the law.
9. How can I distinguish Charles's Law from Boyle's or Gay-Lussac's Law in exam questions?
Charles's Law focuses on the relationship between volume and temperature at constant pressure. Boyle's Law relates volume and pressure at constant temperature. Gay-Lussac's Law connects pressure and temperature at constant volume. Carefully examine which variables are held constant in the problem to determine which law applies.
10. Does Charles's Law apply to liquids or solids in any way?
While Charles's Law primarily describes gases, the principle of thermal expansion applies to liquids and solids as well. However, the relationship is not as simple or direct as for gases. Liquids and solids expand less significantly with temperature changes than gases because of stronger intermolecular forces.
11. What are some applications of Charles' Law in daily life?
Besides hot air balloons, Charles's Law is relevant in various applications including: weather forecasting (changes in air volume due to temperature affect pressure systems); designing engines (managing gas expansion and contraction within cylinders); and industrial processes (controlling gas volume in chemical reactions).
