Answer: 2.58 days
Explanation:
Expression for rate law for first order kinetics is given by:
 
where,
k = rate constant  = ? 
t = age of sample  = 6 days
a = initial amount of the reactant  =  1 g
a - x = amount left after decay process  
= 0.2 g
a) to find the rate constant
 
 
 
b) for completion of half life:  
Half life is the amount of time taken by a radioactive material to decay to half of its original value.
 
 
The half life is 2.58 days
 
        
             
        
        
        
Answer: No.
Explanation: One mole of zinc is not the same as one atom of zinc. In one mole of zinc, there are approximately 6.022*10^23 atoms of zinc.
 
        
             
        
        
        
The molarity is calculated using the following rule:
molarity = number of moles of solvent / volume of solution (in liters)
We have the volume of solution = 250 ml = 0.25 liters and the molarity = 3 m
Substituting in the equation, we get:
3 = number of moles / 0.25
number of moles = 3 x 0.25 = 0.75 moles
        
             
        
        
        
Answer: 1.5 moles
Explanation: one mole Zn uses 2 moles HCl.
1.5 moles Zn uses 3.0 mol HCl. Then Zn is a limiting reactant
And produces equal amount of H2.
 
        
             
        
        
        
Answer: The Lattice energy is the energy required to separate an ionic solid into its component gaseous ions <em>or</em>
It is the energy released when gaseous ions combine to form an ionic solid. 
Explanation:
The lattice energy depends on the ionization energies and electron affinities of atoms involved in the formation of the compound. The ionization energies and electron affinities also depends on the ionic radius and charges of the ions involved. As the ionic radius for cations <em>increases</em> down the groups, ionization energy <em>decreases</em>, whereas, as ionic radii <em>decreases</em> across the periods , ionization energy <em>increases</em>. The trend observed for anions is that as ionic radii <em>increase </em>down the groups, electron affinity <em>decreases. </em>Across the period, as ionic radii <em>increases</em> electron affinity <em>increases</em>. Also, as the charge on the ion <em>increases,</em> it leads to an <em>increase</em> in energy requirement/content.
Therefore, for compounds formed from cations  and anions in the same period, the highest charged cation and anion will have the highest lattice energy. For example, among the following compounds: Al2O3 (aluminium oxide), AlCl3 (aluminium chloride), MgO, MgCl2 (magnesium chloride), NaCl, Na2O (sodium oxide); Al2O3(aluminium oxide) will have the highest lattice energy, thus will be hardest to break apart because its ions have the highest charge.