Find the mass in grams of hydrogen gas produced when 14.0 moles of hcl is added to an excess amount of magnesium.

14.0 g of hydrogen gas

The equation for the reaction is

Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g)  

From the equation, 2mol HCl will produce 1 mol H2

Moles of HCl =14 moles

Therefore; 14 moles of HCl will produce 7 moles of hydrogen gas

1 mole of Hydrogen gas = 2.0 g/mol

Thus; mass of 7.0 moles of H2 = 7 × 2.0 g/mol

                                                   = 14.0 g

when 25.0 ml of 0.700 mol/l naoh was mixed in a calorimeter with 25.0 ml of 0.700 mol/l hcl, both initially at 20.0 °c, the temperature increased to 22.1 °c. the heat capacity of the calorimeter is 279 j/°c.

the equation for the reaction is:

naoh + hcl → nacl + h₂o

moles of hcl = 0.0250 l hcl ×

0.700

mol hcl

1 l hcl = 0.0175 mol hcl

volume of solution = (25.0 + 25.0) ml = 50.0 ml

mass of solution = 50.0 ml soln ×

1.00

ml soln

= 50.0 g soln

δt=t2-t1

= (22.1 – 20.0) °c = 2.1 °c

the heats involved are

heat from neutralization + heat to warm solution + heat to warm calorimeter = 0

q1+q2+q3=0

nδh+mcδt+cδt=0

0.0175 mol ×

δh

+ 50.0 g × 4.184 j·g⁻¹°c⁻¹ × 2.1 °c + 279 j°c⁻¹ × 2.1 °c = 0

0.0175 mol ×

δh

+ 439.32 j + 585.9 j = 0

0.0175 mol ×

δh

= -1025.22 j

δh=1025.22j0.0175 mol= -58 600 j/mol = -58.6 kj/mol

a polar bond is formed when electrons are shared unevenly between atoms