HESI A2 Exam: Gas Laws
• What is Boyle’s Law?
• What is Charles’ Law?
• What is the proportional relationship between volume and pressure?
• What is the equation we need to know for calculating the relationship between pressure and volume?
• What is the new temperature when 2.00 L at 294 K is compressed to 1.00 L (answer below)?
If the temperature is held constant, the pressure of a gas increases as its volume decreases. The reverse is also true; as the pressure of a gas decreases, its volume increases. This is Boyle's Law.
When using Boyle's Law, it is understood that the quantity and temperature of the gas remain constant.
In the late 1700s, Jacques Charles researched the relationship between the temperature of a gas and its volume. He discovered that if the pressure of a gas is held constant, as that gas is heated, its volume will increase. The reverse of that is also true: cooling a gas will cause its volume to decrease. This relationship is known as Charles' Law.
Pressure and volume are inversely proportional to each other, so as the volume increases, the pressure decreases.
Math Problems
2000 mL of a gas at 25 atm is compressed to 1000 mL. What is its new pressure?
In this situation, the volume of a gas is halved, so the pressure needs to double (remember that pressure and volume are inversely proportional to each other). 50 atm is the correct answer.
A gas occupies 11.2 liters at 0.860 atm. What is the pressure if the volume becomes 15.0 L?
The equation we need to know for calculating the relationship between pressure and volume is P1V1 = P2V2, with 1 representing before and 2 representing after. You will always be given three of the variables and have to solve for the fourth variable.
(11.2 liters) (0.860 atm) = (x) (15.0 L)
x = 0.642 atm
500.0 mL of a gas is collected at 745.0 mmHg. What will the volume be at standard pressure (760 mmHg)?
The equation we need to know for calculating the relationship between pressure and volume is P1V1 = P2V2, with 1 representing before and 2 representing after. You will always be given three of the variables and have to solve for the fourth variable.
(745.0 mmHg) (500.0 mL) = (760.0 mmHg) (x)
x = 490.1 mL
What is the new temperature when 2.00 L at 294 K is compressed to 1.00 L.
V1/T1 = V2/T2, with kelvin (K) being a measure of temperature. "1" represents the initial volume or temperature, while "2" represents the final volume or temperature.
(2.00 L) / 294.0 K) = (1.00 L) / (x)
Cross multiply
2x = 293
x = 147.0 K
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