gcse chem- just confused about moles and avagdros constant n how it relates to C-12..

I'm just confused about moles and Avogadro's constant n how it relates to C-12 and where the volume=moles*24 equation comes from?

Thanks so much in advance... I have my chemistry mock very soon!!!

Hello, moles is a tricky one at GCSE so I don't blame you about being confused!!

Moles is a unit of measurement, this wasn't made clear to me when I was learning it, it is the measurement for 'amount of substance'. Just like you would have 10mm in a cm, there are 6.02 x 10^23 particles in 1 mole. It is also important to point out that the measurement of a mole isn't specific to atoms, I use the word particle because the mole could measure atoms, protons, neutrons, electrons, molecules, etc.

Avogadro's constant is just the number 6.02 x 10^23.

From what I can recall, there isn't a link between C-12 and the mole but maybe that is something to do with a different exam board, I did aqa, maybe someone else may know.

The moles equation for a gas is volume= moles x 24dm^3 (or 24000cm^3). This is because at room temperature and pressure, 1 mole of a gas occupies 24dm^3. Therefore, using this idea, if you have 2 moles it will occupy 48dm^3, and 3 moles will occupy 72dm^3 etc. That is why you multiply the number of moles by 24 (or 24,000).

Hope this helps you, just do your best in your mock, I was never happy with my mocks but it pushed me to try even harder for the real thing and I came out with a grade I was really happy with. Let me know if there is anything I haven't been clear about or can answer for you.

Let me know if there is anything I haven't been clear about or can answer for you.

Would you be able to help me out with something else too? I'm just confused about exothermic and endothermic reactions because an exothermic reaction needs more heat energy to 'make the bonds than break the bonds', what does that mean? Ty!! xx

In exothermic and endothermic reactions, energy is required to make bonds, and energy is released when bonds are broken.
In an exothermic reaction, the combined energy released when the bonds of the reactants which are broken is greater than the energy used to make the bonds of the products. This means you have spare energy left over when you do the reaction, which is released into the environment.

To put it simply:
• Exothermic reaction: energy released when the bonds are broken is greater then the energy required to make the bonds later on, so meaning there is an excess of energy.

• Endothermic reaction: energy released when the bonds are broken is less than the energy required to make the bonds later on, meaning there is a lack of energy to make the bonds of the products of the reactants.

OK, Student01234 has answered a lot of this correctly. On the C-12 thing, it's how relative atomic mass is measured. Carbon-12 atoms are taken to have a mass of exactly 12 by definition, with atoms of other elements being measured relative to that. So hydrogen atoms have a mass very close to a twelfth of that (and you can take their mass as being 1 for calculations) but it's not exactly one.

A mole of a substance will have a mass of the R.A.M. number in grams. So a mole of Carbon 12 weighs 12 grams. Does that help?

ohhh tysm!!!!!

Would you be able to help me out with something else too? I'm just confused about exothermic and endothermic reactions because an exothermic reaction needs more heat energy to 'make the bonds than break the bonds', what does that mean? Ty!! xx

ohhh I get it. So, for example, oxygen has a mass of 16g? Tysm for your explanation!! x

I would like to add, my teacher told me a way to remember the difference between exothermic and endothermic reactions: Bendo Pendo, Mexo Nexo.