first-order 2 A(g) → X(g) + 1/2 Y(g) half-life 19.0 min
Consider the hypothetical first-order reaction
2 A(g) → X(g) + 1/2 Y(g)
At a certain temperature, the half-life of the reaction is 19.0 min.
A 1.00-L flask contains A with a partial pressure of 622 mmHg.
If the temperature is kept constant,
what are the partial pressures of A, X, and Y after 42 minutes?
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1차 반응의 반감기
t_1/2 = 0.693 / k
( 참고 https://ywpop.tistory.com/26 )
k = 0.693 / 19.0 min
= 0.03647 /min
Let, certain temperature = 1 K
PV = nRT 로부터,
n / V = P / RT
= (622/760) / 0.08206
= 9.973 M
= [A]_0
1차 반응 속도식
ln([A]_t / [A]_0) = –k•t
[A]_t = e^(–k•t) × [A]_0
= e^(–0.03647×42) × 9.973
= 2.156 M
ICE 도표를 작성하면,
...................... 2 A(g) ..... → ..... X(g) ... + ... 1/2 Y(g)
초기(M): 9.973 ....................... 0 ................... 0
변화(M): –2x .......................... +x .................. +1/2 x
평형(M): 9.973 – 2x .......... x ..................... 1/2 x
[A]_t = 2.156 M 이므로,
[A]_t = 9.973 – 2x = 2.156
2x = 9.973 – 2.156
x = (9.973 – 2.156) / 2
= 3.909 M = X
9.973 – 2x
= 9.973 – 2(3.909)
= 2.155 M = A
3.909 / 2 = 1.955 M = Y
정리하면,
A = 2.155 M
X = 3.909 M
Y = 1.955 M
[참고] 교재 정답에 맞추면,
A = 134 M
X = 244 M
Y = 122 M
A = 134 M 일 때, X는?
2.155 : 3.909 = 134 : ?
? = 3.909 × 134 / 2.155 = 243.1 M
A = 134 M 일 때, Y는?
2.155 : 1.955 = 134 : ?
? = 1.955 × 134 / 2.155 = 121.6 M
[키워드] 1차 반응 기준
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