Horizontal pressure gradient forces are generated within thermal circulations because: o cold air rises and warm air sinks. o aloft, high pressure develops in cold air regions while low pressure develops in warm air regions o at the surface, high pressure develops in warm air regions while low pressure develops in cold air regions o in cold regions, isobars bunch closer together, while in warm regions, they spread farther apart

a corroding iron, if that's one of your choices

it's c (engineer's do their work with mechanical stuff not on any living being)

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