1. Element X has a mass of 300g and a ½ life of 10 years. How many grams will remain after 40 years? Hint: first determine how many ½ lives there are in 40 years

The amount of element X remain after 40 years is 18.75 grams

Explanation:

We are given:

Total time period = 40 years

One half life = 10 years

Calculating the number of half lives,

To calculate the amount of element X after 4 half lives, we use the equation:

where,

a = amount of X after n-half lives

= initial amount of X = 300 g

n = number of half lives = 4

Putting values in above equation, we get:

Hence, the amount of element X remain after 40 years is 18.75 grams

petroleum? coal maybe?

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