Question

Which of the following denotes standard pressure?
A)$\text{ 760 kPa }$
B)$\text{ 760 mm of Hg }$
C) $\text{ 760 atm }$
D) $\text{ 1 torr }$

Answer 1

HINT: pressure is defined as the force exerted per unit area. Pressure can be expressed in various units. The standard state condition is the standard conditions where the pressure of the gas is equal to 1 $\text{ atm }$, the temperature is equal to $\text{ 298 K }$ for the one mole of gas.

Complete step by step answer:
A thermodynamic system is well explained by the four quantities of gas. These are:

1. Temperature of gas
2. Volume of the gas
3. Moles of gas
4. Pressure of the gas
   Any object exerts a force on the surface that comes in contact with it. For example, the balloon in the air exerts the force on the internal surface of the balloon, or force is exerted on the piston of the syringe; the liquid in the syringe exerts the force on the internal surface of the syringe. If the air in the balloon is heated then the gas acquires the kinetic energy and bursts. The pressure is defined as the force exerted per unit area. The pressure is written as follows,
   $\text{ P = }\dfrac{\text{Force}}{\text{Area}}\text{ = }\dfrac{F}{A}\text{ }$
   Standard pressure can be determined by the barometer. It is a long tube that is closed at one end. The tube is filled with the mercury and placed upside down in the dish and allows the air to enter through the tube. The pressure exerted by the mercury in the column is expressed as $\text{ P = }\rho \text{gh }$ where, g is the gravitational acceleration, $\text{ }\rho \text{ }$ is density and h is the height of the mercury in the column. In normal conditions, the force of the air and the force of gravity are balanced when the mercury rises to a height of 760 mm in the column. Thus 1-atmosphere pressure is expressed as 760 mm of Hg. Thus the standard pressure is equal to 760 mm of Hg.

Hence, (B) is the correct option.

Note: the force is expressed as the newton per meter square and area is expressed as the square meter. Thus the SI units of force are given as $\text{ 1 N / }{{\text{m}}^{\text{2}}}\text{ }$ . One $\text{ 1 N / }{{\text{m}}^{\text{2}}}\text{ }$is known as the 1 pascal. There are other units of pressure are as follows,

& \text{ }1\text{ atm = 760 mm of Hg } \\\ & \text{ = 760 torr} \\\ & \text{ = 1}\text{.01325 }\times \text{ 1}{{\text{0}}^{\text{5}}}\text{ Pa} \\\ & \text{ = 101}\text{.325 kPa } \\\ \end{aligned}$$