7 is atomic symbol 9 is atomic density 8 is the atomic number
        
             
        
        
        
The answer for the following problem is mentioned below.
- <u><em>Therefore 298.44 grams of mercuric oxide is needed to produce 0.692 moles of oxygen molecule </em></u>
Explanation:
Given:
no of moles of the oxygen gas = 0.692
Also given:
2 HgO  → 2 Hg + 
where,
HgO represents mercuric oxide 
Hg represents mercury
  represents oxygen
 represents oxygen
To calculate:
Molar mass of HgO:
Molar mass of HgO = 216 grams
molar mass of mercury (Hg) = 200 grams
molar mass of oxygen (O) =16 grams
HgO = 200 +16 = 216 grams
We know;
        2×216 grams of HgO   →  1 mole of oxygen molecule
              ?                              →  0.692 moles of oxygen molecule
        
           = 
       = 298.944 grams of HgO
<u><em>Therefore 298.44 grams of mercuric oxide is needed to produce 0.692 moles of oxygen molecule </em></u>
<u />
 
        
                    
             
        
        
        
Answer:
1400KJ/mol⁻¹
Explanation:
Amount of heat required can be found by:
Q = m × c × ΔT
<em>Where m is the mass, c is the specific heat capacity (4.2KJ for water) and ΔT is the change in temperature.</em>
Q = 24 × 4.2 × (23 - 9)
 = 24 × 4.2 × 14
 =   1411.2KJ/mol⁻¹ 
 = <u>1400KJ/mol⁻¹</u>  (to 2 significant figures)