Ideal gas equations

Hi there, i have been set a homework for ideal gas equations and I have done questions 1-5 (see attachment) but I can't seem to be able to work out how to work out the rest the answers are in the attachment but I can't work out how to do it :

these are the questions, many thanks in advance

6. At 25 oC and 100 kPa a gas occupies a volume of 20 dm3. Calculate the new temperature of the gas if
a) the volume is decreased to 10 dm3 at constant pressure.
b) the pressure is decreased to 50 kPa at constant volume.

7. 10.0 g of calcium nitrate is heated at 100 kPa and a temperature of 300 oC, at which temperature it fully decomposes. Calculate
a) the volume of nitrogen dioxide evolved
b) the volume of oxygen evolved
c) the total volume of gas evolved
Equation: 2Ca(NO3)2(s) → 2CaO(s) + 4NO2(g) + O2(g)

8. Calculate the volume of oxygen produced at 298 K and 100 kPa by the decomposition of 30 cm3 of 0.1 moldm-3 hydrogen peroxide.
Equation: 2H2O2(aq) → 2H2O(l) + O2(g)

9. Lead (IV) oxide dissolves in concentrated hydrochloric acid according to the following equation: PbO2(s) + 4HCl(aq) → PbCl2(s) + Cl2(g) + 2H2O(l)
Starting with 37.2 g of lead (IV) oxide, calculate:
a) the volume of 12 moldm-3 HCl needed to completely dissolve it
b) the mass of PbCl2 produced
c) the volume of chlorine produced at 298 K and 100 kPa.

10. What mass of magnesium, and what volume of 2.0 moldm-3 hydrochloric acid, will be required to produce 100 cm3 of hydrogen gas at 298 K and 100 kPa?
Equation: Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g)

11. 0.52 g of sodium was added to 100 cm3 of water. Calculate:
a) The volume of hydrogen evolved at 298 K and 100 kPa
b) The concentration of the sodium hydroxide solution produced, assuming the volume of water does not change.
Equation: 2Na(s) + 2H2O(l) → 2NaOH(aq) + H2(g)

1.2 Exercise 3 - ideal gas equation.doc28.7KB

maxpark3r

6. At 25 oC and 100 kPa a gas occupies a volume of 20 dm3. Calculate the new temperature of the gas if
a) the volume is decreased to 10 dm3 at constant pressure.
b) the pressure is decreased to 50 kPa at constant volume.

The gas laws are all goverened by the equation:

PV = nRT

------------------------------------------------
If the pressure and moles of gas are constant then:

V/T = constant

Hence:

V1/T1 = V2/T2

-------------------------------------------------

If the volume and moles of gas are constant then:

P/T is constant

and

P1/T1 = P2/T2

-------------------------------------------------

maxpark3r

7. 10.0 g of calcium nitrate is heated at 100 kPa and a temperature of 300 oC, at which temperature it fully decomposes. Calculate
a) the volume of nitrogen dioxide evolved
b) the volume of oxygen evolved
c) the total volume of gas evolved
Equation: 2Ca(NO3)2(s) → 2CaO(s) + 4NO2(g) + O2(g)

Work out moles of gases from moles of calcium nitrate used. Then use

PV = nRT

to work out volume.

maxpark3r

8. Calculate the volume of oxygen produced at 298 K and 100 kPa by the decomposition of 30 cm3 of 0.1 moldm-3 hydrogen peroxide.
Equation: 2H2O2(aq) → 2H2O(l) + O2(g)

Moles of H2O2 from molarity x volume (litres)

Then as above Q7

maxpark3r

9. Lead (IV) oxide dissolves in concentrated hydrochloric acid according to the following equation: PbO2(s) + 4HCl(aq) → PbCl2(s) + Cl2(g) + 2H2O(l)
Starting with 37.2 g of lead (IV) oxide, calculate:
a) the volume of 12 moldm-3 HCl needed to completely dissolve it
b) the mass of PbCl2 produced
c) the volume of chlorine produced at 298 K and 100 kPa.

a)
1. mol of lead (IV) oxide = mass/Mr
2 equation coefficients to find mol equivalent mol of HCl from equation stoichiometry
3. mol = MV to get V for HCl

b) equation coefficients to find mol equivalent

c) equation coefficients to find mol equivalent then PV = nRT

maxpark3r

10. What mass of magnesium, and what volume of 2.0 moldm-3 hydrochloric acid, will be required to produce 100 cm3 of hydrogen gas at 298 K and 100 kPa?
Equation: Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g)

By now you should have the idea...

maxpark3r

11. 0.52 g of sodium was added to 100 cm3 of water. Calculate:
a) The volume of hydrogen evolved at 298 K and 100 kPa
b) The concentration of the sodium hydroxide solution produced, assuming the volume of water does not change.
Equation: 2Na(s) + 2H2O(l) → 2NaOH(aq) + H2(g)

ditto...

(edited 14 years ago)

Reply 2

maxpark3r

OP

2

Thanks very much, i will give this a go

Reply 3

maxpark3r

OP

2

Using your methods i'm still unable to do it, i'm very confused

maxpark3r

Using your methods i'm still unable to do it, i'm very confused

Take one question at a time and show us your working...

Reply 5

Anas99

can you do question 7 step by step please

Reply 6

Pigster

20

Nice searching skills, that's a five year old thread you've found.

What's so difficult?

Work out the amount of reactant, from that you can work out the amount of each product and then using the IGE, work out the volumes (although you'll only have to do that once).

Reply 7

drakee

Pv = nRT
APPLIED ONLY TO IDEAL GASES

P is pressure and measured in Pascals (pa)
v is volume and measured in meters cube
n is no moles
n is the gas constant and has the value of 8.31
AND
T is temperature that is measured in Kelvins

just put all the values and find the unknown out of them

If you want to get tough at this then you need to practice lots of past paper questions and I have recently discovered one site where you would be able to get them in bulk form as well.....
aolpapers.com
Hope helps you

(edited 9 years ago)

Reply 8

Anas99

Original post by charco

Take one question at a time and show us your working...

on question 7 would you divide 10g by the mr of calcium nitrate to get the moles and then times the answer by 2 as theres a 2 to 4 ratio between calcium nitrate and no2. then would you just sub this mole answer into the gas equation.

Original post by Anas99

on question 7 would you divide 10g by the mr of calcium nitrate to get the moles and then times the answer by 2 as theres a 2 to 4 ratio between calcium nitrate and no2. then would you just sub this mole answer into the gas equation.