Energy change & Rates of reaction

Chemistry

What do all chemical reactions involve as bonds are broken and formed?

-All chemical reactions involve changes in energy as bonds are broken and formed

what does ΔH (the overall energy change of a reaction) depend on?

ΔH = energy absorbed (break the bond) - energy released (form the bond)

lil side note: ΔH is basically just change in chemical potential energy or just energy during a reaction.

Exothermic and endothermic reactions

depend on wether or not there is a net release or net absorption of energy

Exothermic reactions

-Chemical potential energy is converted to thermal energy

-Thermal energy is then released into the surroundings

-This results in a net release of energy (ΔH < 0) to form the bond

-The net release of thermal energy into the surroundings causing surrounding temperature to increase.

-As a result the products have lower energy than reactants

Endothermic Reactions

-Thermal energy is absorbed from the surroundings

-This thermal energy is then converted into chemical potential energy

-This results in a net absorption of energy (ΔH> 0) to break the bond.

-There is an absorption of thermal energy from the surroundings

-As a result the products have higher energy than the reactants

Do stronger bonds require more energy to break and release more energy when formed?

Yes.

What makes a bond endothermic?

Breaking bonds require energy to break

What makes a bond exothermic?

Forming bonds releases energy and is exothermic.

What can energy changes in reactions be represented by?

By using an energy profile.

On an energy profile diagram, where is the activated complex found?

-At the peak of the curve

What is the activation on an energy profile diagram?

-The activation energy is the difference between the reactants and the activated complex

What is change in enthalpy (ΔH) on an energy profile diagram

-It is the difference in energy between the reactants and the products

Relationship between reactants and products in exothermic reactions

-In exothermic reactions more energy is released to form the bond (than absorbed) and therefore the reactants are greater than the products in exothermic reactions

Relationship between reactants and products in endothermic reactions

-In endothermic reactions more energy is absorbed than released to break a bond therefore the energy of the reactants is less than the energy of the products.

Rate of reaction

The speed at which reactants are converted to products

What are some examples of reactions that take place very rapidly

-Precipitaion reactions, the neutralisation of an acid with a base,

What are some examples of reactions that take place very slowly?

-The rusting of iron

-zinc dissolving in acid (this reaction takes place more moderately)