Se dice que una sustancia sufre cambios químicos cuando: a. desaparece.
b. se forman sustancias diferentes.
c. no se altera su identidad.
d. no hay cambios visibles.

answer

i think the answer is a) as air pressure in an area increases, the density of the gas particles in that area decreases.

hope it

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

i believe the answer is 5,000