Reaction Rate

Reactant A can participate in both of these reactions: 1) A + B --> C + D TriGrxn = -15.6 kJ 2) A + E --> F + G TriGrxn = -20.5 kJ Reaction 1 has a much higher rate than Reaction 2 under the same reaction conditions. Explain this observation in terms of activation energy.

Higher activation energies generally lead to lower reaction rates. Reaction 2 has a lower reaction rate than Reaction 1. The activation energy for Reaction 2 is probably higher than that for Reaction 1.

Hydrogen peroxide (H2O2) readily decomposes to form water and oxygen gas: 2H2O2(aq) → 2H2O(l) + O2(g) What concentration of hydrogen peroxide would cause this reaction to proceed most quickly?

30%

Select the correct collision theory explanation for changing the rate of the given chemical reaction.

Particles collide with less force - Refrigerate food to keep it from spoiling. Particles collide less frequently - Add inert water to a reaction solution. Particles collide more frequently - Compress the air/fuel mixture inside an engine cylinder with a piston. - Grind a metal into a fine powder. Particles collide point of water with a pressure cooker. - Raise the boiling point of water with a pressure cooker.

Food spoils because of chemical reactions. Many types of spoilage occur because of the actions of microorganisms, such as bacteria. These organisms, like all organisms, rely on chemical reactions within their bodies to carry out their life processes. Based on this information, what is the most likely reason that refrigerating most foods reduces the rate at which they spoil?

The lower temperature reduces molecule speeds, reducing the number of effective collisions.

Reactions occur at the surface

increasing the surface area increases particles available for reaction decreasing the particle size increases the surface area.

When A + B is at low range and C is higher

the reaction progression is nonspontaneous

When A + B is at mid range and C is a little under A + B

the reaction progression is spontaneous

When A + B is mid range and C is lower

the reaction progression is spontaneous

Acid rain is a dilute solution of acids that dissolve the calcium carbonate in limestone statues. Concentrated acids can dissolve a large piece of limestone in a few days. Statue breakdown due to acid rain can take decades, but statues with intricate carvings break down more quickly. Explain these observations in terms of reaction rates.

the time taken for the statue to break down depends on the reaction rate the low concentration of acids in acid rain reduces the reaction rate and increases the time required to break down the statue intricate carvings increase the surface area of the surface area of the statue and therefore increase the rate of the statue's breakdown.

To make gas reaction go faster

Add reactants Decrease Volume

Which reactions are likely to be self-sustaining?

Burning gasoline in a car engine. Thrusting a rocket into space. NOT an hard-boiled egg.

Side note

Increasing pressure increases reaction rate if the reactants contain more moles of gas than the products

Due to lower atmospheric pressure at high altitudes, water boils at 92°C instead of 100°C. How will this difference affect cooking times? How will it affect the time needed to boil spaghetti noodles as compared to the amount of time needed at sea level?

It will be longer.

What conditions will cause a reaction to occur?

Particles and molecules must collide. Collisions must be energetic enough to overcome the activation barrier. Collisions must be properly oriented for the relevant parts to react. The energy needed to overcome the activation energy comes from the kinetic energy of random.

The diagram shows energy for reactions A and B. Reaction A (orange) is lower than reaction B (blue).

They both has the same reaction so neither is higher. Reaction B has the higher activation energy. Reaction A will most likely proceed faster.

2SO3(g) ---> 2SO2(g) + O2(g) Na2CO3(s) + 2HCl(aq) ----> CO2(g) + H2O(l) + 2NaCl(aq)

decreased rate

N2(g) + 3H2(g) ---> 2NH3(g)

increased rate

For reactions involving gases

increasing pressure increases concentration, which increases reaction rate.

SnO2(s) + 2H2(g) ---> Sn(s) + 2H2O(g) AgNO3(aq) + Cu(s) ---> CuNO3(aq) + Ag(s)

no change in rate

A chemical engineer is developing a process for producing a new chemical. One step in the process involves allowing a solution of potassium hydroxide to react with a solid. Which action would most likely increase the reaction rate for this step?

using a more concentrated potassium hydroxide solution.

Magnesium reacts with hydrochloric acid to form hydrogen gas and magnesium chloride: Mg(s) + 2HCl(aq) ---> MgCl2(aq) + H2(g) Which actions would increase the rate of reaction?

using hot hydrochloric acid solution using magnesium powder instead of a large piece of magnesium