6E Hess's Law - Edexcel IAS Chemistry (Unit 2)

[@hanamostafa5268]

21:51/ why here we placed the delta H with - value why not +283 and +890 as it was in the question?

[@MissNatalieChemistry]

Hello Hana, the question should have negative signs before each of those values - they have not shown up on the video correctly. Apologies for that. Remember that an enthalpy of combustion value will always be negative as it is always an exothermic reaction. I hope that helps!

[@hanamostafa5268]

@@MissNatalieChemistry Ohh right it is an exothermic reaction... Thx soo much

[@deenamirza322]

At 30:30 mins, why do we add a positive sign at the end of the answer? Isn't standard enthalpy change of neutralisation an exothermic process? I'm confused.

[@nho2x113]

in 25:32 why are there 3 arrows?? and can the arrow be from anywhere of the equation or we must point the 5O2 to the 4H2O and so on

[@user-mc9it4yb3y]

29:55 here, how did you calculate the value of n? Thanks a lot! your videos are of tremendous help!

[@MissNatalieChemistry]

The n value (or number of moles) is calculated by dividing the mass of sodium hydrogencarbonate used (8g) by the molar mass (84g) and you get 0.095238 moles. Apologies that this wasn't clear in the video.

[@dxrk7958]

Please can u do more hard questions because I'm really struggling with this I couldn't do a single question from hess law

[@MissNatalieChemistry]

I will be adding more past paper questions for Unit 2 in the coming weeks, please check back soon.

[@dxrk7958]

@@MissNatalieChemistry trust me I'm really active on ur channel

[@AOXZ1]

Why is there a third arrow at 25:32 please reply ASAP

[@fachispitis6363]

Can you please help me solve the 3rd question in that chapter's checkpoint.

[@RinoGu]

17:35 how abt the oxygen from H2 + O2 --> 2H2O? why isnt that O2 not included ard the arrow

[@Lily108y]

I’m finding this topic very difficult I got the worked examples but I’m still a little confused with question d) in January 2019 25:32

[@MissNatalieChemistry]

What part of the question are you unsure about?

[@Lily108y]

@@MissNatalieChemistry the enthalpy change past paper question in 25:32

[@MissNatalieChemistry]

@@Lily108y But is there a specific part of question you don't understand. It's a similar Hess's Law question to the others.

[@Phoenixwinsx]

@@MissNatalieChemistry you are amazing. Thank you so so much for doing what you do. You're a hero, saving lives out here.

[@TheNoobHamster]

@@Phoenixwinsx No prob fam, anytime 💪 stay hard out there son.

[@zaminhaqqani3487]

How do you know which ones the target equation?

[@MissNatalieChemistry]

You are always told in the question what you are trying to calculate.

[@kuromi7151]

25:14 why's there a third arrow 4 x Hc (H2) if it's already in the box (4H2) ??

[@AOXZ1]

im curious about that too

[@minalhq5762]

isnt this a different method than what the other boards use? they have seperate cycles for combustion and formation

[@ruthikaajit2767]

Hi, how do you know where the arrows are pointing to in the cycle

[@nethuwankuranage6941]

if its burned or neutralised arrows are pointed towards the product if formed arrows are pointed to theproduct formed

[@hanamostafa5268]

26:38 why here we started from the intermediate box and not from the reactant like from propran-1-ol and oxygen? Isnot that what hess law says "we have to start from the reactant to the product "?

[@MissNatalieChemistry]

Hello Hana, here we are filling in the intermediate box as part of the question. The arrows will point up towards the reactants and products as we are using the Enthalpy of Formation values. This means our intermediates are the elements needed in the formation of each of the reactants and products. You are correct that Hess's Law refers to the reactants to the products but that doesn't affect the direction of the arrows in this question. Once we have the cycle set up, then we can follow the arrows or flip them as necessary to answer the question. I hope that helps!

[@hanamostafa5268]

@@MissNatalieChemistry Thanks for your respond but you didn't catch up my question....I mean why,when u calculated the enthalphy change of formation for propan-1-ol you started (you made the large red dot)from the intermediates and not the reactants and you said that this path (from intermediates to products) is the same as from the intermediates to products.That's what i didn't get... like Isn't Hess's law says that enthalphy change will always be equal even if we took alternative paths between the reactants and the products (but you started from the intermediate box in ur path not the reactants) I hope u got my question.. ! and thanks for your answer anyways :)

[@rhythmnafi5646]

The formula fr molar enthalpy is minus Q by n right? bt in one worked example u didnot use the negative sign..why? plz explain

[@MissNatalieChemistry]

The negative sign can be used in the equation but you can also wait and add it in at the end. It doesn't make a difference. As long as the negative sign is included for exothermic reactions, you will get the mark.

[@rhythmnafi5646]

@@MissNatalieChemistry thank u so much maam ur videos saved my u4 chem ..its so resourceful and easier to understand and the last part of the videos with pp is the big plus point and the notes are so organised ... Thank You

[@snappy.r6875]

In 13:14 the worked example 2 we are breaking a compound into oxides. But isnt ∆fH for elements in standard states. How is CaO & CO2 an element I'm a bit confused here any help would be highly appreciated 😊😊

[@vyic3073]

19:19 what about oxygen

[@Miko-orginal-1]

This is so fun

[@farhanimran6407]

this topic is so confusing i have my exam on monday i still cant understand

[@justsomeone2001]

How’d it go?

[@dearlantsov]

the arrows and which direction they're gonna point to always confuses me😵

[@hanamostafa5268]

@miss natalie chemistry please help?!

[@oongaboonga3014]

Wargaye