Energy Changes 2:Question 1
When a 25.7 g sample of Nal dissolves in 80.0 g of water in a
calorimeter, the temperature rises from 20.5 °C to 24.4 °C. (specific
heat for water = 4.18 J/g °C). How much heat did the reaction
generate?
Select one
1.304 J
418 J
1,952 J
8159 J

answer : third trial had the contaminated sample and the correct value for dhrxn should be 1000 kj/mol

explanation :

let us write down the given equations

equation 1 :

equation 2 :

equation 3 :

let us use hess's law to find out which 2 equations can be added to get the third equation.

let us reverse equation 2 and multiply it by 2. the new equation that we get is,

equation 4 :

let us add equation 1 & 4

the above equation is similar to equation 3 but has different value for dhrxn.

therefore third trial had the contaminated sample and the correct value for dhrxn should be 1000 kj/mol