An unknown metal displaces aluminum (Al) from solution but does not displace sodium (Na). Using the activity series, determine the unknown
metal.
A calcium (Ca)
B. zinc (Zn)
C. manganese (Mn)
D. magnesium (Mg)

what is the general relationship between a galaxy's distance from earth and its speed?

the answer is:

the farther away a galaxy is from us, the faster it is moving away from us.

your answer is a. the enthalpy of formation for a pure element in its standard state is always positive.

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