How did the experiement with boiling water compare with the experiment in which magnesium was added to hydrochloric acid? both resulted in gas formation. both resulted in temperature change. both involved chemical change. both involved physical change. one involved chemical change while the other involved physical change.

Answer is:

Both resulted in gas formation.

Both resulted in temperature change.

One involved chemical change while the other involved physical change.

1) Balanced chemical reaction of magnesium and hydrochloric acid:

Mg + 2HCl → MgCl₂ + H₂(g).

Hydrogen(H₂) is a gas. This is exothermic reaction (energy is released). This is chemical change, new substances are formed.

2) Boiling water is physical change, no new substances are formed. This is endothermic reaction, heat is added. Steam is gas.

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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