Chemical Reactions Intro

Chemicals reactions

Introduction

Matter Transformations

Physical changes are limited to changes that result in a difference in display without changing the composition. Some common changes (but not limited to) are:

• Texture
• Color
• Temperature
• Shape
• Change of State (Boiling Point and Melting Point are significant factors in determining this change.)

A chemical change occurs when the substance's composition is changed. When bonds are broken and new ones are formed a chemical change occurs. The following are indicators of chemical changes:

• Change in Temperature
• Change in Color
• Noticeable Odor (after reaction has begun)
• Formation of a Precipitate
• Formation of Bubbles

Chemical Reactions

A chemical reaction is in which the bonds are broken within reactant molecules, and new bonds are formed within product molecules in order to form a new substance.A new compound (product) results from a chemical change as the atoms rearrange themselves to form new chemical bonds. A chemical change always involves a chemical reaction.

• Burning wood
• Souring milk
• Mixing acid and base
• Digesting food

• Cooking an egg
• Heating sugar to form caramel
• Baking a cake
• Rusting of iron

Collision and kinetic-molecular theories

The collision theory is based on the assumption that for a reaction to occur it is necessary for the reacting species (atoms or molecules) to come together or collide with one another. Not all collisions, however, bring about chemical change. A collision will be effective in producing chemical change only if the species brought together possess a certain minimum value of internal energy, equal to the activation energy of the reaction.

The kinetic-molecular theory explains how the atoms and the molecules of the different chemical compounds are in continuous motion and that if this movement increases, the energy and the possibility of collisions increase; therefore, in the gaseous state there is more kinetic energy that is associated with movement and facilitates the formation of new substances

chemical kinetics

Chemical kinetics can be used to describe and analyse the velocity at which reagents react and the speed at which products are produced in a given time interval. The speed of reactions may be affected by factors such as:

Surface AreaWhen solids and liquids react, increasing the surface area of the solid will increase the reaction rate. A decrease in particle size causes an increase in the solid’s total surface area.

Concentration RateWhen the concentrations of the reactants are raised, the reaction proceeds more quickly. This is due to an increase in the number of molecules that have the minimum required energy

CatalystSubstance that changes speed of chemical reaction without undergoing a permanent chemical change

Reactives' NatureFor a chemical reaction to take place, it is important to know the chemical properties and reactivity of the reagents.

Temperature Raterate constant must increase with increasing temperature, thus increasing the rate of reaction

Parts of a Chemical Equation

Coefficient

State of matter

Separation of R and P

Heat

Reactants

Products

Gas or Precipitate

Subscript

Produces