ΔH = -1204 kJ 3.55 g Mg(s) –234 kJ 40.3 g MgO(s)

ΔH = -1204 kJ 3.55 g Mg(s) –234 kJ 40.3 g MgO(s)

 

 

Consider the following reaction:

2Mg(s) + O2(g) → 2MgO(s) ... ΔH = -1204 kJ

 

a) Is this reaction exothermic or endothermic?

b) Calculate the amount of heat transferred

when 3.55 g of Mg(s) reacts at constant pressure.

c) How many grams of MgO are produced

during an enthalpy change of -234 kJ?

d) How many kJ of heat are absorbed

when 40.3 g of MgO(s) is decomposed

into Mg(s) and O2(g) at constant pressure?

 

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a) Is this reaction exothermic or endothermic?

 

ΔH < 0 이므로, 발열 (exothermic).

( 참고 https://ywpop.tistory.com/9152 )

 

 

 

 

b) Calculate the amount of heat transferred

when 3.55 g of Mg(s) reacts at constant pressure.

 

Mg의 몰질량 = 24.31 g/mol 이므로,

3.55 g / (24.31 g/mol) = 0.146 mol Mg

( 참고 https://ywpop.tistory.com/7738 )

 

 

2Mg(s) + O2(g) → 2MgO(s) ... ΔH = -1204 kJ

---> Mg 2 mol 반응 시, ΔH = -1204 kJ 이므로,

 

2 mol : -1204 kJ = 0.146 mol : ? kJ

? = (-1204) × 0.146 / 2 = -87.9 kJ

 

 

 

 

c) How many grams of MgO are produced

during an enthalpy change of -234 kJ?

 

2 mol : -1204 kJ = ? mol : -234 kJ

? = 2 × (-234) / (-1204) = 0.389 mol MgO

 

 

MgO의 몰질량 = 40.30 g/mol

0.389 mol × (40.30 g/mol) = 15.7 g MgO

 

 

 

 

d) How many kJ of heat are absorbed

when 40.3 g of MgO(s) is decomposed

into Mg(s) and O2(g) at constant pressure?

 

2MgO(s) → 2Mg(s) + O2(g) ... ΔH = +1204 kJ

 

 

MgO의 몰질량 = 40.30 g/mol

40.3 g / (40.30 g/mol) = 1.00 mol MgO

 

 

2 mol : 1204 kJ = 1.00 mol : ? kJ

? = 1204 / 2 = 602 kJ