In order to get the sum of 2.7 and 2.47, we will add both numbers. So, 2.7 plus 2.47 would be 5.17. And the correct number of significant digits in this number is still the same, 5.17, so we have three significant numbers. Why? There are three rules in identifying the significant figures: 1. Non zeros are always significant (which this applies in our sum above). 2. Any zeros in between significant numbers are always significant. 3. <span> The final zero or zeros in the decimal portion only are significant.</span>
Avogadro’s constant tells us the number of atoms in a mole of any substance: 6.022x10^23. A mole of water, oxygen, sodium - they all have this many atoms in a 1 mole sample.
A 0.5 mole sample of helium gas would contain 0.5 x (6.022 x 10^23) atoms, or 3.011 x 10^23 atoms. Still a big amount.
The
equilibrium constant is a value which represents the equilibrium of a reaction.
It is a reaction quotient when the reaction reached equilibrium. The reaction in the system is expressed as:
<span>H2 + I2 = 2HI
we express Keq as follows:
Keq = [HI]^2 / [H2] [I2]
Where the terms represents the concentrations of
the substances involved. THe concentrations are as follows:</span>
<span>H2 = 0.763 ( 1 / 18.02) / 3.67 = 0.0115 M</span>
<span>I2 = 96.9 ( 1 / 253.8) / 3.67 = 0.1040 M</span>
<span>HI (at equilibrium) = 90.4 ( 1 / 127.91) / 3.67 = 0.1956 M</span>
<span>
By the ICE table, we can calculate the
equilibrium concentrations,
H2 I2 HI
I 0.0115 0.1040 0
C -x -x +2x
-----------------------------------------------------------
E 0.0115-0.0963 0.1040-0.0963 0.1926 ===> x = 0.0963
Keq = (</span>0.1926<span>)^2 / (0.0077) (0.0848)
Keq = 56.81</span>
If the half-life of a sample of a radioactive substance is 30 seconds, how much would be left after 60 seconds? <span>
A. one-fourth</span>