Answer
5
Work Step by Step
Palmitic acid combustion:
$C_6H_{32}O_2(s)+13\ O_2(g)\rightarrow 6\ CO_2(g)+16\ H_2O(g)$
Enthalpy:
$6\times-393.509+16\times-241.83-$
$-848.4=-5383\ kJ/mol$;
$-5383\ kJ/mol\div 136.32\ g/mol=$
$-39.5\ kJ/g$
Starch combustion:
$C_6H_{10}O_5(s)+6\ O_2(g)\rightarrow 6\ CO_2(g)+5\ H_2O(g)$
Enthalpy:
$6\times-393.509+5\times-241.83-$
$-960=-2610\ kJ/mol$;
$-2610\ kJ/mol\div 162.14\ g/mol=$
$-16.10\ kJ/g$
Per peanut:
$0.73\ g\times (49/100\times-39.5\ kJ/g+21/100\times-16.10\ kJ/g)=-16.60\ kJ$
Heat required:
$250\ mL\times 1\ g/mL\times 4.184\ J/g.K\times (100-25)\ K=78.45\ kJ$
Peanuts required:
$78.45/16.60=4.72$
5 peanuts required.
