When a chemical system is at equilibrium, Multiple Choice the forward and reverse reactions have stopped. the concentrations of the reactants are equal to the concentrations of the products. the concentrations of the reactants and products have reached constant values. the reaction quotient, Q, has reached a maximum.

if you mean hydrogen and oxygen then water is the product

d

explanation:

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