# chemistry

Consider the first order reaction A --> products where 25% of A disappears in 24 seconds. What is the half life of this reaction?

...i thought it would just be doubled but it isn't. i'd appreciate an explanation.

1. 👍
2. 👎
3. 👁
1. Probably I work these the long way but I do that because then I know I will get it right.
ln(No/N) = kt
I assume a value of 100 for No, and if 25% disappears, that means 75% is left so starting with 100 gives me 75 at the end of 24 seconds.
ln(100/75) = 24*k
solve for k and I get 0.01199 (I know that's too many places but I just leave those numbers in the calculator. Then for the half life
ln(100/50) = 0.01199t1/2
solve for t1/2
Check my math but I obtained 57.8 seconds which would be rounded to 58 sec if the 24 value has just 2 s.f.

1. 👍
2. 👎

## Similar Questions

1. ### chemistry

The rate constant for this first-order reaction is 0.320 s–1 at 400 °C. A--> Products How long (in seconds) would it take for the concentration of A to decrease from 0.830 M to 0.220 M?

2. ### science

Q.1 Cellular respiration is an exothermic reaction and photosynthesis is an endothermic reaction. How does the required activation energy compare for these two reactions? 1. Cellular respiration needs a smaller amount of energy to

3. ### chemistry

The rate constant for this first-order reaction is 0.0570 s–1 at 400 °C. A-->Products After how many seconds will 14.0% of the reactant remain?

4. ### Chemistry

The rate constant for this first‑order reaction is 0.340 s−1 at 400 ∘C. A⟶products How long, in seconds, would it take for the concentration of A to decrease from 0.620 M to 0.280 M?

1. ### Physical Science

Which of the following statements are true about chemical reactions? Check all that apply. A. Reactants are on the right when writing a chemical reaction. B. Products are produced in a reaction. C. Reactants are present at the end

2. ### Chemistry--need help!

1. Which of the following statements is true about reaction rates? a. Reaction rates can be predicted from the coefficients of the balanced equation. b. Reactants usually disappear faster than the products appear. c. Reactants

3. ### chemistry class

A flask is charged with 0.124 mol of A and allowed to react to form B according to the reaction A(g) → B(g). The following data are obtained for (A) as the reaction proceeds: Time (s) 1 10 20 30 40 Moles of A 0.124 0.110 0.088

4. ### Chemistry

In the first order, reaction A yields products, A=0.400M initially and 0.250M after 15.0 min. What is the value of the rate constant, k?

1. ### Rate Laws

If the initial concentration of AB is 0.210 M, and the reaction mixture initially contains no products, what are the concentrations of A and B after 75 s? The reaction is in the second order: rate=k[AB]^2 The rate constant is

2. ### ENZYMS

Q.1 Cellular respiration is an exothermic reaction and photosynthesis is an endothermic reaction. How does the required activation energy compare for these two reactions? 1. Cellular respiration needs a smaller amount of energy to

3. ### Chemistry

The rate constant for the reaction 2A → B is 7.63 × 10−3 s−1 at 110°C. The reaction is first order in A. How long (in seconds) will it take for [A] to decrease from 1.17 M to 0.590 M?

4. ### Chemistry

Before a chemical reaction reaches equilibrium, A. the reaction rates of the reactants and products increase. B. the reaction rate of the reactants increases and the reaction rate of the products decreases. C. the reaction rates