When you are balancing chemical reactions (equations'), what must you never touch? the normal-looking numbers to the left of the molecules or compounds. the coefficients, the numbers in subscript

The correct answer option is: the number in subscript.

When you are balancing any chemical equation, you must never touch or change the number in subscript of the molecule of a chemical or compound as it will upset the composition.

the numbers in subscript

Explanation:

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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