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How do you decide what the sign of the enthalpy change should be?

You have to think about whether or not energy is being released by the system into the surroundings (exothermic), or whether the system is taking energy up from the surroundings (endothermic).You have to put...
BW
Answered by Ben W. • Chemistry tutor
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Calculate the percentage composition by mass of Lithium Sulfate, Li2SO4.

(Taken from GCSE WJEC Additional Science Book- First Published in 2012) and I have adapted the answer given.Relative atomic masses: Li = 7 ; S= 32 ; O=161) Calculate molecular mass of lithium sulfate (Li2SO4...
EL
Answered by Elinor L. • Chemistry tutor
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What is the electronic configuration of Calcium?

Calcium has 20 electrons. The first ring can only contain up to 2 electrons.After that rings can only contain up to 8 electrons. Therefore the electronic configuration of Calcium would be: [2, 8, 8, 2]
JM
Answered by Jonny M. • Chemistry tutor
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Define and then compare the periodic table trends (atomic radius, electronegativity, ionization energy, electron affinity) for Lithium (Li) and Sodium (Na).

The Atomic radius of an atom represents its atomic size. More specifically, it refers to the half-distance between the two nuclei of two adjacent atoms of the same element. In the periodic table, across a pe...
DA
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Acid HA has a Ka of 2.00 x 10-4mol dm-3. A solution was made by adding 15cm3 of 0.34 M NaOH to 25cm3 of 0.45M HA. Calculate the moles and the concentration of A- and HA in this solution. Using the expression for Ka calculate the pH of the solution

Write the equation : NaOH + HA --> NaA + H 2 O. Find the moles of A - : the moles of A - = the moles of NaOH added. 15 x 10 -3 x 0.34= 5.10 x 10 -3 . Workout the initial moles of HA : 25 x 10 -3 x 0.45= 0...
HS
Answered by Hibba S. • Chemistry tutor
7377 Views