Urgent: Chem Help!!! (1 Viewer)

[starryXnite]

i've got my chem prelim tomorrow and i was wondering what calculations should i know and how the calculations work...coz i kinda get mixed up with which calculation is which

can u help me plz???

its really urgent

 

[bubblesss]

i've got my chem prelim tomorrow and i was wondering what calculations should i know and how the calculations work...coz i kinda get mixed up with which calculation is which

can u help me plz???

its really urgent

just know ur mles stuff and balanced equations and all the formulae.

 

[starryXnite]

oh ok thks bubblesss...

i have studied for my prelim im just abit lost with the formulas

by the way have u done ur chem prelim yet?

 

[ratcher0071]

i've got my chem prelim tomorrow and i was wondering what calculations should i know and how the calculations work...coz i kinda get mixed up with which calculation is which

can u help me plz???

its really urgent

-specific heat capacity
-moles --> mass (and vice-versa)
-concentration/molarity

 

[kaz1]

You have to know how to calculate the empirical formula as well.

 

[katie tully]

Dude tbh I have no idea what the OP is asking.

Like. What have you done in Prelim Chem for the past 9 months?

 

[starryXnite]

so its formulas like

n=m/M & c=n/V i need to know?

 

[tommykins]

yes

 

[kaz1]

so its formulas like

n=m/M & c=n/V i need to know?

Yes. But don't forget AH=mcAt (A is delta).

 

[ratcher0071]

so its formulas like

n=m/M & c=n/V i need to know?

yeah and also:

delta h = -mCdelta T
molarity = Energy (kJ) / moles (mol)

 

[starryXnite]

delta h = -mCdelta T
molarity = Energy (kJ) / moles (mol)

i dont think i have learnt these yet...
do you think it will be in the prelims...

ive only done the chemical earth, metals,water and half way through energy...
could that be why i havent learnt the formulas above?

 

[kaz1]

delta h = -mCdelta T
molarity = Energy (kJ) / moles (mol)

i dont think i have learnt these yet...
do you think it will be in the prelims...

ive only done the chemical earth, metals,water and half way through energy...
could that be why i havent learnt the formulas above?

You should have learned those formulas in the Water Module.

 

[starryXnite]

wait...i think i did do molarity but ive never seen the delta formula
whats the delta formula for?

 

[kaz1]

wait...i think i did do molarity but ive never seen the delta formula
whats the delta formula for?

Calculating the change in heat(in joules); m is the mass of the water in grams, c is a constant(4.18), delta t is the final temperature minus the initial temperature.

 

[ratcher0071]

wait...i think i did do molarity but ive never seen the delta formula
whats the delta formula for?

delta h = enthalpy change / heat energy (absorbed or released)
m= mass
C= specific heat capacity
delta T = change in temperature

 

[ratcher0071]

Calculating the change in heat(in joules); m is the mass of the water in grams, c is a constant(4.18), delta t is the final temperature minus the initial temperature.

Doesn't always have to be 4.18 kaz1, that's only the specific heat capacity for water

 

[starryXnite]

um..im really sry kaz and ratcher but im still kind of confused about the delta formula do u think you could explain it to me again?

what would usually be given to you if you were to solve a question with the delta formula?

also what is the delta formula used to find?

 

[ratcher0071]

um..im really sry kaz and ratcher but im still kind of confused about the delta formula do u think you could explain it to me again?

what would usually be given to you if you were to solve a question with the delta formula?

also what is the delta formula used to find?

For example:

You are given 100g of Water, the temperature changes from 20^oC to 30^oC calculate the amount of heat energy needed to invoke this change in temperature?

Use formula:
delta h = mCdelta T
delta h = 100 x 4.18 (Specific heat capacity of water) x (30-20)
delta h = 418 x 10
delta h = 4180 Joules

 

[kaz1]

Doesn't always have to be 4.18 kaz1, that's only the specific heat capacity for water

That's the only heat capacity you need to know in the syllabus.

um..im really sry kaz and ratcher but im still kind of confused about the delta formula do u think you could explain it to me again?

what would usually be given to you if you were to solve a question with the delta formula?

also what is the delta formula used to find?

You should look up enthalpy in your textbook. I'm sure the textbook can explain it better than I can.

 

[starryXnite]

thank you kaz and ratcher

this helps me alot...

oh um... last question what does the formula

c1V1=c2V2 relate to and how is it used?