Classify each of the following as either a physical change or a chemical change. a. tearing a sheet of paper,
b. melting a piece of wax,
c. burning a log

A:Physical, B:Both, C: Chemical

Explanation:

Tearing paper is physical because only the appearance has changed. Melting wax can be either physical or chemical depending on whether the wax actually burns or not, burning a log is chemical because new substances are formed when wood burns.

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