11 Part A Energy in Reactions

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this reaction is endothermic

2NH3(g) + 92.4 kj => N2 (g) + 3H2 (g)

A catalyst speeds up a reaction

by lowering the required activation energy

An inhibitor slows down a reaction

by raising the activation energy

For an Exothermic reaction, the change in enthalpy (delta H) is

negative

For an Endothermic reaction, the change in enthalpy (delta H) is

positive

Collision theory

reactions occur as a result of collisions between the reactants.

In an Endothermic Reaction, energy is ...

... absorbed

In an Endothermic reaction, the temperature inside the reaction vessel...

... becomes cooler.

In an Exothermic reaction, the temperature inside the reaction vessel...

... becomes warmer.

Activation Energy ...

... is always a positive number. D H in this reaction is positive (endothermic)

Exothermic Reaction, energy is ...

... is released.

Exothermic Reaction

Energy is a product of the reaction.

Endothermic Reaction

Energy is a reactant of the reaction.

Temperature affects reaction rate

If temperature is increased, the reaction will be quicker. Faster moving particles collide more often, and more particles will have enough energy (Ea) when they collide

Definition of Activation Energy (Ea)

The minimum amount of energy required for a reaction to occur.

5 basic ways to speed up a reaction

Increase collisions by: temperature; Surface Area; Concentration. Reduce activation energy by using a Catalyst. Nature of the reactants

Surface Area of the reactants affects reaction rate

More exposed particles causes more collisions, so there will be more collisions with the correct orientation

this reaction is exothermic

N2 (g) + 3H2 (g) => 2NH3(g) + 92.4 kj

Concentration of reactants affects reaction rate

Number of particles in a given volume affects rate of concentration - more particles, more collisions

Catalyst

Reduces the activation energy of a reaction and speeds the reaction up without being used up in the process

Activation Energy

The energy from the peak of the reaction minus the energy in the reactants.

Change in enthalpy (delta H)

The energy of the products minus the energy of the reactants.

Nature of the reactants affects reaction rate

The rate of a chemical reaction depends on the medium in which the reaction occurs. It may make a difference whether a medium is aqueous or organic; polar or nonpolar; or liquid, solid, or gaseous, reactive or non-reactive.

Activated complex (Transition state)

a short lived intermediate substance that occurs at the peak energy of the reaction. It lasts for 10 -13 seconds. It is an arrangement of the atoms somewhere between the reactants and the products.

In an Endothermic reaction, the energy of the reactants is ____ than the energy of the products

greater

In an Exothermic reaction, the energy of the reactants is ____ than the energy of the products

less


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