8. [06.02]
on a potential energy diagram, what type of reaction will always have the reactants at a higher potential
energy than the products? (2 points)
o
exothermic reaction
o
endothermic reaction
synthesis reaction
single replacement reaction

Exothermic reaction  

Explanation:

Consider the reaction

A + B ⟶ C

If energy is released, the product C is at a lower potential energy level than the reactants A and B (see diagram).

Conversely, the reactants A and B are at a higher energy level than the product.

B is wrong. In an endothermic reaction, the reactants A and B are at a lower energy level than the product.

C and D are both wrong. Both types of reaction can be exo- or endothermic.

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