Predict the temperature change?

Question

Predict how the temperature change that you measure for 25 mL of 2 M NaOH added to 25 mL of 2 M hydrochloric acid compare to the temperature change when 25 mL of 1 M NaOH is added to 25 mL of 1 M hydrochloric acid.



a

The measured temperature change will be lower

b

The measured temperature will be the same

c

The measured temperature change will be higher

d

Cannot predict

Answer 1

NaOH(aq) + HCl(aq) ==> NaCl(aq) + H2O(l) ... balanced equation for neutralization

q = mC∆T where q = heat; m = mass; C = specific heat; ∆T = change in temperature

25 ml 2 M NaOH + 25 ml 2 M HCl = 50 mmol NaOH + 50 mmol HCl => 50 mmole H2O ∆H = x

25 ml 1 M NaOH + 25 ml 1 M HCl = 25 mmol NaOH + 25 mmol HCl => 25 mmole H2O ∆H = 1/2x

The measured temperature change will be twice as great for the first reaction compared to the second reaction because twice as many moles are reacting and twice as many moles of product are produced. So answer (c).