 # How to find the number of atoms in a substance

## How to find the number of atoms in a substance

Specific analysis is needed. In a word, first calculate the amount of molecular material, and then calculate the total number of atoms according to the molecular structure

### How to judge the number of molecules and atoms? Is the number of atoms the sum of the subscripts under matter?

As many moles as there are
The number of atoms in a molecule is the sum of the subscripts multiplied by the number of molecules

### Among the following groups of substances, the one with the same number of molecules and atoms is () A: 0.5mol hydrogen and 0.5mol oxygen B: 1mol hydrogen chloride and 1mol carbon dioxide C: 1mol water and 1mol ammonia D: 1mol water and 1mol carbon dioxide

A
The molecular number is the 23rd power of 0.5 * 6.02 * 10
The atomic number is 2 * 6.02 * 10 to the 23rd power

### The density ratio of 2molo3 and 3molo2 at the same temperature and pressure is? What is the volume ratio?

At the same temperature and pressure, the volume of O3 and O2 is 22.4l/mol, so the volume of 2molo3 is 44.8l
The volume of 3molo2 is 67.2l, so the volume ratio is 2:3, and the mass fraction of O3 is 48g / mol
The mass fraction of O2 is 32g / mol, and the density ratio at the same temperature and pressure is 48:32 = 3:2

### What is the average molecular weight of the gas after 3molo2 and 2molo3 are mixed?

The total mass of mixed gas is m = 3x32 + 2x48 = 192g
The amount of total substance is n = 2 + 3 = 5mol
Therefore, the average molar mass m = m / N = 192 / 5 = 38.4g/mol
We know that the relative molecular mass is equal to the molar mass of the material
Therefore, the average relative molecular weight of the mixed gas is 38.4

### What are the mass ratio, molecular number ratio and oxygen atom number ratio of 2molo3 to 3molo2? The mass ratio of 2molo3 to 3molo2 is ____; The ratio of the number of molecules is _____; The ratio of the number of oxygen atoms is _____

The mass ratio of 2molo3 to 3molo2 is__ 1：1_________； The ratio of molecules is___ 2：3__________； The ratio of oxygen atoms is__ 1：1______________.