Which statement is true of a chemical reaction? A.) energy is not Transferred. B.) energy is always released.
C.) energy is either released or absorbed.
D.) energy is always absorbed.

the answer is: they rebelled against saddam hussein’s rule.

kurds opposed saddam rule and wanted independence. kurds in the north and shiites in the south revolt against hussein.

for example, the halabja attack in 1988 conducted against the kurdish people by the iraqi regime under saddam hussein, where between 4000 people are killed and around 9000 are injured.

the enthalpy of formation of water is given as -285.8kj/mol, which states that the enthalpy of formation is negative.

negative enthalpy of formation indicates that the heat is released during the reaction process. the heat is released from reaction to the surroundings the enthalpy is expressed with a negative sign with the energy given out in the reaction process.

the formation of water takes place by giving out heat which is -285.8 kj/mol.

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