Mendeleev · Chemistry pathway · level 2

Ideal gas: understanding PV = nRT

The ideal-gas model links pressure, volume, amount of substance and absolute temperature. It is very useful but remains an approximation.

The essential idea

The ideal-gas model links pressure, volume, amount of substance and absolute temperature. It is very useful but remains an approximation.

Example

At fixed amount and volume, increasing absolute temperature increases pressure in the ideal model.

Mini problem

Why must kelvins be used in PV = nRT?

Show the solution

Because the equation uses absolute temperature, whose zero corresponds to thermodynamic zero.

Common mistake

Do not replace reasoning with a memorized rule. Always check geometry, units, coefficients or model assumptions.

Guided exercise

At fixed volume and amount of gas, what happens to pressure when absolute temperature rises from 300 K to 600 K?

Show the detailed solution

In the ideal model, P is proportional to T under these conditions. Doubling T therefore doubles pressure.

Avoid this

Do not substitute 27 °C for 300 K in a temperature ratio: gas laws use absolute temperature.

Go further

Ideal gas Temperature converters

Mini lab

At fixed volume and amount, what happens to pressure?

Initial T (K) Initial P (bar) New T (K)

New pressure2.00 bar

P₂ = P₁ × T₂/T₁ here because V and n are fixed.

Key idea

Ideal gas: understanding PV = nRT

Put it into practice · V/V₀1

Key idea

Ideal gas: understanding PV = nRT

PV = nRT

Before moving on, explain “Ideal gas: understanding PV = nRT” in two sentences without rereading the page. Then give one concrete example.

Guided example

Ideal gas: understanding PV = nRT

Before moving on, explain “Ideal gas: understanding PV = nRT” in two sentences without rereading the page. Then give one concrete example.

Put it into practice

Ideal gas: understanding PV = nRT

Choose a concrete case linked to Ideal gas: understanding PV = nRT. Write down the known information, what you are trying to find, and the units. Then state the rule, model or trend you will use. If a calculation is involved, keep the units visible at every line; if it is conceptual, state what changes and what remains fixed.

Check your answer

A strong answer contains four things: the starting situation, the variable that changes, the direction or numerical result, and one check. The check can be a unit, an order of magnitude, a limiting case or a comparison with a familiar example.

Periodic table