0.64 M citric acid 5.00 mL 0.77 M NaOH 45.00 mL 26.0℃ 27.9℃

0.64 M citric acid 5.00 mL 0.77 M NaOH 45.00 mL 26.0℃ 27.9℃

 

 

Citric acid has three dissociable hydrogens.

When 5.00 mL of 0.64 M citric acid and 45.00 mL of 0.77 M NaOH

at an initial temperature of 26.0 °C are mixed,

the temperature rises to 27.9 °C as the citric acid is neutralized.

The combined mixture has a mass of 51.6 g

and a specific heat of 4.0 J/g•°C.

Assuming no heat is transferred to the surroundings,

calculate the enthalpy change for the reaction

of 1.00 mol of citric acid in kJ.

 

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

 

[1] 수용액이 흡수한 열

q = C m Δt

( 참고 https://ywpop.tistory.com/2897 )

 

= (4.0 J/g•°C) (51.6 g) (27.9 - 26.0 °C)

= 392.16 J

---> 반응계가 방출한 열 = -392.16 J

 

 

 

[2] citric acid의 몰수

(0.64 mol/L) (5.00/1000 L) = 0.0032 mol citric acid

 

 

 

[3] NaOH의 몰수

(0.77 mol/L) (45.00/1000 L) = 0.03465 mol NaOH

 

 

 

[4] citric acid : NaOH = 1 : 3 mol비로 반응하므로,

 

C6H8O7 + 3NaOH → Na3C6H5O7 + 3H2O

( Na3C6H5O7의 구조식 https://ywpop.tistory.com/3636 )

 

citric acid : NaOH = 1 : 3 = 0.0032 mol : ? mol

? = 3 × 0.0032 = 0.0096 mol NaOH

---> NaOH는 반응하고도 남는다.

= citric acid는 전부 반응했다.

 

 

 

[5] 몰당 반응열을 계산하면,

-392.16 J / 0.0032 mol

= -122550 J/mol

= -122.550 kJ/mol

 

 

 

답: -123 kJ (1.00 mol당)

ΔH < 0 이므로, 발열 반응.

 

 

 

[키워드] 구연산 기준문서, 구연산 + NaOH, citric acid + NaOH, C6H8O7 + NaOH, 구연산의 해리, 구연산의 이온화, 구연산은 3가산, 구연산은 삼가산