Calculate the number of kilojoules to warm 125 g of iron from 23.5°c to 78.0°c.

            Q  =  3.06 kJ

Solution:

The equation used for this problem is as follow,

                                                 Q  =  m Cp ΔT   (1)

Where;

           Q  =  Heat  =  ?

           m  =  mass  =  125 g

           Cp  =  Specific Heat Capacity  =  0.450 J.g⁻¹.°C⁻¹

           ΔT  =  Change in Temperature  =  78.0 °C - 23.5 °C  =  54.5 °C

Putting values in eq. 1,

                            Q  =  125 g × 0.450 J.g⁻¹.°C⁻¹ ×  54.5 °C

                            Q  =  3065 J

Or,

                            Q  =  3.06 kJ

as given the equation is

2al + 6 hcl > 2 alcl3 + 3 h2(g)

as per equation two moles of aluminum reacts with six moles of hcl to give two moles of alcl3 and three moles of hydrogen gas

given: three moles of al are present and 7 moles of hcl

for three moles of aluminum nine moles of hcl will be required

however as 7 moles of hcl are present so the limiting reagent is hcl

hcl is going to decide the number of moles of product formed

when six moles of hcl are present = 3 moles of h2 are formed

when one mole of hcl is present == 3/6 mole sof h2 will be formed

when 7 moles of hcl are present = 3 x 7/ 6 moles of h2 will be formed = 3.5 moles of h2

answerlinnaeus;