Question

1.621 g of glucose (MW=180g/mol) is introduced into a calorimeter containing 100g water. When the sugar sample is burned completely in the calorimeter, the water temp is observed to increase by 5.4°C. Determine specific heat sH (c) for the reaction in kJ per mole of sugar.

Answer 1

Mass of water, m_w = 100 g

Specific of water , C_pw = 4.184 J/g-K

rise in the temperature, T = C or 5.4 K

so, amount of heat energy released, q_w = mC_pwT

= 100*4.184 * 5.4 = 2259.63 J = 2.26 kJ

so, this amount of energy will be also associated with glucose,

as given , mass of glucose , m_g = 1.621 g

So, number of moles of glucose, n = 1.621/180 = 9*10^-3 mole

só, 9 * 10^-3 mole absorb 2.26 kJ of energy,

so, specific heat of glucose in terms of kJ per mole , sH(c)= 2.26 / (9*10^-3) = 250.92 kJ per mole