One of these has a negative value for (triangle) H. select the correct one

The methane gas burns

Explanation:

The burning of methane gas is a combustion reaction. Combustion is an exothermic process. For all exothermic processes, ∆H is negative.

Combustion reaction involves the evolution of heat. The energy of reactants is greater than the energy of products hence the excess energy is given off in the form of heat leading to a negative value of the enthalpy of reaction, hence the answer.

answer: any goods being imported from another country may be subject to issued by the federal government are tariffs

explanation:  

tariffs are a tax on anything that are imported from abroad. government use them to protect and boost their local industries and the thought is that they encourage consumers to buy local instead of importing and they will hope will protect jobs and economy in the country that implements them  

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