Reaction order/constant, time dependent pressure

In summary, the conversation discusses a problem from a graduate textbook about chemical kinetics. The problem involves measuring the rate of a reaction and determining the order of the reaction and the specific rate constant. The conversation also addresses the importance of the initial pressure of 55 mm Hg and how it relates to the reaction stoichiometry. The conversation concludes with the suggestion to use chemical calculators and titration methods to solve the problem.
  • #1
Animastryfe
81
0
This isn't a homework question per se, but it is from a (graduate) textbook. I'm not taking a course in this, but I've been trying to learn some basic chemical kinetics and couldn't find other problems like this one.

Homework Statement


The rate of the reaction

CH5NH2(g) -> C2

H4(g) + NH3(g) is measured by noting Ptotal as a function of time. At 500 degrees celsius, the following results were obtained:
Time (sec): 0 60 360 600 1200 1500
Ptotal (mm Hg): 55 60 79 89 102 105

a: Find the order of the reaction.
b: Find the specific rate constant.

Homework Equations



The Attempt at a Solution



At first, I thought that this was a straightforward question asking me to use the integrated rate equations and graphing to find k, but then I noticed that, although pressure can be substituted for concentration (I think?) in this case, what was measured isn't the decrease in reactant, but rather increase in product. However, I don't understand the importance of the pressure of 55 mm Hg at t=0. I suppose I can't just use the difference between two Pts as x, the decrease in reactant. It's been a while since I've taken general chemistry, so any help is appreciated.
 
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  • #2
55 mmHg reflects initial amount of the substance that decomposes (there is some typo in the formula). Later observed pressure is sum of both reactants and products. You can calculate partial pressures using reaction stoichiometry (how many moles of each product per every mole of reactant decomposed?).

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methods
 
  • #3
Borek said:
55 mmHg reflects initial amount of the substance that decomposes (there is some typo in the formula). Later observed pressure is sum of both reactants and products. You can calculate partial pressures using reaction stoichiometry (how many moles of each product per every mole of reactant decomposed?).

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chemical calculators - buffer calculator, concentration calculator
www.titrations.info - all about titration methods

Ah, thank you. I haven't done these kind of questions for a while, so thinking about calculating partial pressure didn't even occur to me until much later. So the 55 mm Hg at t=0 is the pressure of the sole reactant before the reaction starts? I'll try this again later today.
 

FAQ: Reaction order/constant, time dependent pressure

1. What is the reaction order?

The reaction order is a measure of how the concentration of a reactant affects the rate of a chemical reaction. It can be determined through experimental data and can be either zero, first, or second order.

2. How is the reaction order determined?

The reaction order is determined by plotting the concentration of the reactant against the rate of the reaction. If the graph is a straight line, the reaction is zero or first order. If it is a curve, the reaction is second order.

3. What is the reaction rate constant?

The reaction rate constant is a proportionality constant that relates the concentration of reactants to the rate of the reaction. It is represented by the symbol "k" and has units of concentration per time.

4. How does time affect pressure in a reaction?

In a time-dependent pressure reaction, the pressure of the system changes over time as the reaction progresses. This can be due to the release or consumption of gases, or the change in temperature or volume of the reaction vessel.

5. How is the rate of a reaction affected by pressure?

The rate of a reaction can be affected by pressure in two ways. First, an increase in pressure can increase the rate of reactions involving gases by increasing the number of collisions between molecules. Second, changes in pressure can also alter the equilibrium of a reaction, affecting the rate at which products are formed.

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