When 10cm3 of 1 mol dm^-3 nitric acid is mixed with 20cm3 of 1 mol dm^-3 sodium hydroxide solution, there is a temperature rise of (delta)T.If the reaction is repeated with 20cm3 of nitric acid of 1 mol dm^-3 and 20cm3 of 1 mol dm^-3 sodium hydroxide, the temperature rise is A 2(delta)TB 1.5(delta)TC (delta)T D 0.75(delta)TThe answer is B
In the first reaction, n HNO3 = 0.01 mol and n NaOH = 0.02 mol... Hence n H2O = 0.01 mol as HNO3 is the limiting reagent in this reaction However, when the reaction is repeated, n HNO3 is 0.02 mol, hence n H2O = 0.02 mol So, the amount of energy released will increase by a factor of two
Also, the mass of the system has increased The first reaction involved 30 cm3 of solution, and the second reaction involved 40 cm3 of solution So, the mass has increased by a factor of 34
Since Q=mcΔT, ΔT = mcQ c is constant, hence hasn't increased/decreased between reactions, so can be omitted ∴ ΔT = mQ As you can see, ΔT is proportional to Q and inversely proportional to m... So, ΔT will increase by a factor of two, but decrease by a factor of 34, giving an overall increase of 1.5 Furthermore, you can use the above equation to verify this, by substituting the factors in: ΔT = 4/32=43⋅2=46 = 1.5
Hence, regardless of your approach, you'll see that ΔT has increased by a factor of 1.5