How do you bake bread?
Everybody enjoys the smell and taste of freshlybaked bread. It is light and fluffy as a result of the action of yeast on sugar. The yeast converts the sugar to carbon dioxide, which at high temperatures causes the dough to expand. The endresult is an enjoyable treat, especially when covered with melted butter.
Charles’s Law
French physicist Jacques Charles (17461823) studied the effect of temperature on the volume of a gas at constant pressure. Charles’s law states that the volume of a given mass of gas varies directly with the absolute temperature of the gas when pressure is kept constant. The absolute temperature is temperature measured with the Kelvin scale. The Kelvin scale must be used because zero on the Kelvin scale corresponds to a complete stoppage of molecular motion.
Mathematically, the direct relationship of Charles’s law can be represented by the following equation:
As with Boyle’s law,
Temperature (K)  Volume (mL) 

50  20  0.40 
100  40  0.40 
150  60  0.40 
200  80  0.40 
300  120  0.40 
500  200  0.40 
1000  400  0.40 
When this data is graphed, the result is a straight line, indicative of a direct relationship, shown in Figure below.
Notice that the line goes exactly toward the origin, meaning that as the absolute temperature of the gas approaches zero, its volume approaches zero. However, when a gas is brought to extremely cold temperatures, its molecules would eventually condense into the liquid state before reaching absolute zero. The temperature at which this change into the liquid state occurs varies for different gases.
Charles’s Law can also be used to compare changing conditions for a gas. Now we use
This equation can be used to calculate any one of the four quantities if the other three are known. The direct relationship will only hold if the temperatures are expressed in Kelvin. Temperatures in Celsius will not work. Recall the relationship that K = °C + 273.
Sample Problem: Charles’s Law
A balloon is filled to a volume of 2.20 L at a temperature of 22°C. The balloon is then heated to a temperature of 71°C. Find the new volume of the balloon.
Step 1: List the known quantities and plan the problem.
Known

V1=2.20 L 
T1=22∘C=295 K 
T2=71∘C=344 K
Unknown

V2=? L
Use Charles’s law to solve for the unknown volume
Step 2: Solve.
First, rearrange the equation algebraically to solve for
Now substitute the known quantities into the equation and solve.
Step 3: Think about your result.
The volume increases as the temperature increases. The result has three significant figures.
Summary
 Increasing the temperature of a gas at constant pressure will produce and increase in the volume.
Practice
Perform the calculations at the web site below:
http://mmsphyschem.com/chuckL.pdf
Review
Questions
 Explain Charles’ Law in terms of the kinetic molecular theory.
 Why does the temperature need to be in Kelvin?
 Does Charles’ law hold when the gas becomes a liquid?