Summary Grade 12 IEB Physical Science - Stoichiometry Essentials

T M




consider :
2H (g)>
+
019) -
2H20 (e)



balanced to
must be obey law of conservation of mass the , balancing numbers

mole ratios between reactants and products
represent
-




H2 O2 H2O numbers referred to stoichiometric
(balancing
:
1 2
.
·




as

2 mol I mol 2 mol Coefficients)
-
used in
calculations


1 . Mass-mass calculations



calculate the mass of produced 29
example
oxygen when
4g of potassium
:
,




Chlorate decomposes completely according to the
following balanced
equation .


2k(10g(s) -
> 2k((is) + 30 19) ,




Step 1 Convert the mass to moles (n
given
:




M 39 35 5 3(16) mol
122
59
= + + = .




,
,




n
= =24
Step 2 : use mole ratio between KCIOs Cused) and Oz (formed)

KCLO3 :
Oz
2 mol :
3 mol
1 mol : 1 5 my
.




0 , 24mol :
1, 5 x 0, 24 =
0, 36 mol



Step 3 Calculate
:

the unknown
quantity (mass
o produced

02 M 2(16) mol
32g
: = =
.




M 32x0, 36 11 ,
529
m =
n .
= =

, . Mass-volume
2 calculations


25g of calcium carbonate reacts with excess dilute hydrochloric
example completely
:




balanced equation What
add
according
to the
following volume of carbon
.




dioxide collected at STP gas

CaCOz(s) +
2H(((aq)
-


>
CaCk(aq) + Hc0(1) + CO,
(g)

Step 1 Convert mass to moles (n)
given
:




+
M 40 3(16) mol
12
100g
= + + =
.




n
== =
0, 25



Step 2 : use mole ratio between CaCO3 Cused) and CO2produced


CaCO3 :
CO2
Ima : I mol
0 25 : 0, 25
,




Step 3 : Calculate the unknown
quantity (volume of CO2 produced
V nVm .
=
0 25. x 22 4 =
,
5 6 dm
,




. volume-volume
3 calculations


calculate the volume of
oxygen required
example : to convert 300dms of sulphur
sulphur trioxide at STP .
dioxide completely into



250 - (9) +
02(g) -

250319)

1 Convert volume
Step given to moles (n)
:




n = = = 13 , 393mo



Step 2 : use mole ratio between So, and 02


SO2 :
02
zmal : I mal

13 , 393 : 6 , 697



Step 3 Calculate the unknown
quantity (volume of O2 produced
:




V nVm
.
=
6, 697x22 4 =
150 01am ,
,