Which is sign that work is being done

If it is positive energy it enters the system.If it is negative it leaves the system.Therefore if work is done on the system it's a sign of positive & if work is done by the system its a sign or negative.

Explanation:

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the ratio of the conjugate base to the acid required to attain the desired ph.

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