in excess ? RATE OF REACTION?

[matt123]

Yeah, even though you are adding more HCl, you are increasing the volume too. Hence they negate each other so to speak, and the rate stays the same. However, this is assuming that the added HCl is the SAME concentration of the original HCl in the sample.

If you have a say 100ml 0.5M HCl solution reacting with some mass of CaCO3 and then you add 100mL of 10M HCl, obviously the rate is going to change.

Yeh true.
Already so let me get this straight.
hmm adding more hcl wont change the rate.
What if it WAS NOT in excess?
because
I remember .. " adding more reactants" increases the rate of reaction?
is this not the same thing? adding more reactant HCL .. .??

If it's not in excess then yes. The rate will increase as you add more HCl. Like fady said above. Don't overthink VCE. I know for a fact that many things taught in VCE chem is incorrect and changes when we get to uni chem.

So if its not in excess .... we actually increase the CONCENTRATION by adding more reactants? lol dosnt make sense ? we are adding more MOLS .....? hmm wait ... yeah i guess the concentration does increase .. but volume increases too

hmm wait put it this way
does adding reactants increase the rate of reaction? if so .. why? ( because there is an increase in concentration of reactants???) .... ? whats the diff if one is in excess? .... still increasing the conc lol.. im so lost here.

[3Xamz]

No, if its in excess you ARENT changing the concentration. You are just adding more of it.
Sure you are increasing the number of mol, but you are also increasing the volume. Hence they cancel out.

That's for excess, but if its not in excess sure the above still applies but now they are more mols of it to react. Hence the reaction rate would be altered.

[matt123]

No, if its in excess you ARENT changing the concentration. You are just adding more of it.
Sure you are increasing the number of mol, but you are also increasing the volume. Hence they cancel out.

but if it is NOT in excess.
Adding reactants will increase the rate by increasing concentration??
well you are ALSO increasing the volume LOL
so how does it increase the rate of reaction?

[JinXi]

Yeah, even though you are adding more HCl, you are increasing the volume too. Hence they negate each other so to speak, and the rate stays the same. However, this is assuming that the added HCl is the SAME concentration of the original HCl in the sample.

If you have a say 100ml 0.5M HCl solution reacting with some mass of CaCO3 and then you add 100mL of 10M HCl, obviously the rate is going to change.

Yeh true.
Already so let me get this straight.
hmm adding more hcl wont change the rate.
What if it WAS NOT in excess?
because
I remember .. " adding more reactants" increases the rate of reaction?
is this not the same thing? adding more reactant HCL .. .??

If it's not in excess then yes. The rate will increase as you add more HCl. Like fady said above. Don't overthink VCE. I know for a fact that many things taught in VCE chem is incorrect and changes when we get to uni chem.

So if its not in excess .... we actually increase the CONCENTRATION by adding more reactants? lol dosnt make sense ? we are adding more MOLS .....? hmm wait ... yeah i guess the concentration does increase .. but volume increases too
hmm wait put it this way
does adding reactants increase the rate of reaction? if so .. why? ( because there is an increase in concentration of reactants???) .... ? whats the diff if one is in excess? .... still increasing the conc lol.. im so lost here.

I think it's something along the lines that adding more reactants pushes the reaction foward, thus increasing the rate of reaction.. bit rusty here (when not in excess)

[3Xamz]

Yup, read above I added that bit soon after I posted it ><

[Mao]

Imagine two scenarios:

Vessel 1: 1L vessel, 1M HCl, 0.1M HNO3.

Vessel 2: Exactly the same as vessel 1, but we add 1L of 1M HCl.
This vessel thus has 2L, 1M HCl, 0.05M HNO3
Despite adding 1L of 1M HCl (+ 1 mol), we haven't increased the concentration of HCl because the volume increased proportionally. The reaction rate will actually be LOWER in this second vessel because the concentration of nitric acid is lower.

In general, rate of reaction will only increase if you are adding extremely concentrated reactants.

e.g. 1L of 1M HCl, 0.1M HNO3, we add 100 mL of 10M HCl --> 1.1L of ~2M HCl, ~0.09M HNO3

[JinXi]

Imagine two scenarios:

Vessel 1: 1L vessel, 1M HCl, 0.1M HNO3.

Vessel 2: Exactly the same as vessel 1, but we add 1L of 1M HCl.
This vessel thus has 2L, 1M HCl, 0.05M HNO3
Despite adding 1L of 1M HCl (+ 1 mol), we haven't increased the concentration of HCl because the volume increased proportionally. The reaction rate will actually be LOWER in this second vessel because the concentration of nitric acid is lower.

In general, rate of reaction will only increase if you are adding extremely concentrated reactants.

e.g. 1L of 1M HCl, 0.1M HNO3, we add 100 mL of 10M HCl --> 1.1L of ~2M HCl, ~0.9M HNO3

Typo for your last part. its 0.09M of HNO3, unless I'm missing something.

[3Xamz]

Imagine two scenarios:

Vessel 1: 1L vessel, 1M HCl, 0.1M HNO3.

Vessel 2: Exactly the same as vessel 1, but we add 1L of 1M HCl.
This vessel thus has 2L, 1M HCl, 0.05M HNO3
Despite adding 1L of 1M HCl (+ 1 mol), we haven't increased the concentration of HCl because the volume increased proportionally. The reaction rate will actually be LOWER in this second vessel because the concentration of nitric acid is lower.

In general, rate of reaction will only increase if you are adding extremely concentrated reactants.

e.g. 1L of 1M HCl, 0.1M HNO3, we add 100 mL of 10M HCl --> 1.1L of ~2M HCl, ~0.9M HNO3

Typo for your last part. its 0.09M of HNO3, unless I'm missing something.

Yeah, he's typo-ed there.
Initially - 1L had 0.1M, so .1mol
Finally - 1.1L would have a concentration of (.1/1.1) = 0.09M

[Mao]

Imagine two scenarios:

Vessel 1: 1L vessel, 1M HCl, 0.1M HNO3.

Vessel 2: Exactly the same as vessel 1, but we add 1L of 1M HCl.
This vessel thus has 2L, 1M HCl, 0.05M HNO3
Despite adding 1L of 1M HCl (+ 1 mol), we haven't increased the concentration of HCl because the volume increased proportionally. The reaction rate will actually be LOWER in this second vessel because the concentration of nitric acid is lower.

In general, rate of reaction will only increase if you are adding extremely concentrated reactants.

e.g. 1L of 1M HCl, 0.1M HNO3, we add 100 mL of 10M HCl --> 1.1L of ~2M HCl, ~0.9M HNO3

Typo for your last part. its 0.09M of HNO3, unless I'm missing something.

thank you sir