Exam Walkthrough - Enthalpy Changes

Question covers calorimetry, enthalpy changes of formation and a tricky Hess' law calculation.

[julieazizi]

THANK YOU SIR I JUST SAT MY ALEVELS IN MARCH BECAUSE U ARE TOO GOOD! THEY CHANGED THE SPEC JUST FOR YOU!!! UR A STAR GOD BLESS!!! U BEAUT

[glimmerpearl]

Thank you sir
Your explanation was great and now I have confidence to answer these questions in exam

[OVOTROY]

Why was 3NO positive when its on the side of the reactants??

[farhaanahmed]

Hi Sir,

At 1:10, why is the value of m used, 50g? Like I don't understand why that mass is used as opposed to the mass of both reactants combined?

[rifannizar]

sir i have a doubt
in the equation Q=mc(temp change)
is m only the mass of water and liquids that have same density as water
or the substances added like for example I have a solution of 20cm^3 and I add 4g of FB5( salt Na2A.5H2O)
then do I add the mass of FB5 also to get Q=(20+4)*4.18*(temp change)
or would I just do Q=20*4.18*(temp change)
please answers I have my p3 exam tomorrow

[ishhq_x]

Hello sir,
Why do you use the mass of HCl (50.0g) rather than the mass for Na2CO3 (3.18g)

[OVOTROY]

why did you use sodium carbonate moles when you used the mass of HCL if its in excess why did you use 50g at all??

[Sumi]

Why did you use the mass of Na2CO3 as part of the mols calculation?

[heyitsmenaomi]

Thank you sir but why was there a negative sign for the enthalpy change of reaction. Is it due to the reaction being exothermic and if so how do you ifnd out if a reaction is exo/endothermic

[rayanhelw]

What specification are the questions from?

[akuawinnie]

Hi, will we always have a limiting reagent? if not which reactant do we use for the mole calculation ?

[libbythomas]

Hi, in the first example how do I know I need to put a negative sign in front of my answer. When do I do this?

[tuhfayar]

hello sir
why is it the mass of hcl because m in the equation stands for the mass of water, doesnt it?

[abdullahal-madhi]

hello sir how did you figure the value of 3 at 7:05

[dniilii]

I'm in agony 'cause of dis chemistry shit.😪