Question

The enthalpy of solution of sodium hydroxide is -42.6 kJ.mol-1. What mass of sodium hydroxide would produce a temperature rise of 5.00 K when dissolved in 200.0 cm3 of water?

Answer 1

q = msΔt

mass of solution = mass of water + mass of sodium hydroxide

$m = m_w + m_{sh}$

M(NaOH) = 40 g/mol

n(NaOH) $= \frac{m_{sh}}{40}$

1 mole of NaOH gives heat energy of 44.2 KJ

So, $q = 44200 \times \frac{m_{sh}}{40}$

The heat capacity is 4.184 J/C

$44200 \times \frac{m_{sh}}{40} = (200 + m_{sh}) \times 4.184 \times 5 \\ 1105 \times m_{sh} = 4184 + 20.92 \times m_{sh} \\ 1084.08 \times m_{sh} = 4184 \\ m_{sh} = 3.86 g$

Answer: 3.86 g