Clarissa is conducting an experiment. She carefully measures out 15g of baking soda into a bag. She then carefully measures out 25ml of vinegar (which is equal to 25g), pours the vinegar into the bag and immediately seals it. She then watches bubbles start to form and the bag fills up with gas. According to the law of conservation of mass, how much should the bag weigh after the reaction is finished? 10g
40g
25g
15g

your answer is a. the enthalpy of formation for a pure element in its standard state is always positive.

im pretty sure its b

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