The atomic number of sodium is 11. This tells us that sodium has 11 protons and because it is neutral it has 11 electrons. The mass number of an element tells us the number of protons AND neutrons in an atom (the two particles that have a measurable mass).

5 0

2 years ago

Question 43 please. i’m not sure if i got the right answer

hram777 [196]

a) The reaction is exothermic since the overall enthalpy change is negative. this means that the system has lost energy to the environment, namely, the apparatus and due to drought.

b) We first calculate the number of moles in 3.55 grams of magnesium.

number of moles= mass/ atomic mass

=3.55/24

=0.1479 moles(to 4sf)

now, if 2 moles of magnesium give -1204kJ

How much energy is given by 0.1479 moles

= (0.1479×-1204kJ)

=-89.0358kJ (don't forget the negative sign)

c) two molesof MgO produces -1204kJ of energy

then -234kJ will be produced by

=(-234kJ×2moles)/1204kJ

=0.3887moles

one mole of MgO weighs 24+16=40

therefore the mass produced is 0.3887moles×40=15.548grams

(d) we first find the number of moles of MgO in 40.3 grams

number of moles=mass/RFM

=40.3g/40= 1.0075moles

if 2 moles of MgO give 1204 kJ then decomposing 1.0075 moles requires

(1.0075 moles×1204kJ)/2=606.515kJ

4 0

3 years ago