Investigating Chemical Reactions Chemical reactions are simply processes that involve chemical change. A chemical change is one in which new substances are formed. Mass is conserved in a chemical reaction (Law of Conservation of Mass). This is true since the number of atoms of each element is conserved in a chemical reaction. Chemical equations are used to describe chemical reactions. 9 CHAPTER

Investigating Chemical Reactions There are six common types of chemical reactions. Chemists are able to use these patterns to predict the products of common reactions. Some chemical reactions are slow, some are fast. The rate of a chemical reaction is affected by various factors. These factors include temperature, reactant concentration, surface area of reactants, and the presence of a catalyst. 9 CHAPTER

Investigating Chemical Reactions Activity In groups of two or three, brainstorm 3–4 different clues that may indicate when a chemical change is occurring. What might you sense— see, hear, feel, smell, etc.? Using your clues, determine if a physical or chemical change is taking place when food colouring is added to water. wax cools into a solid. water forms bubbles when boiling. steam releases heat when condensing. What do you think must occur at the molecular level for a change to be a chemical change? See page 232 in the textbook for the difference between a physical and chemical change. 9 CHAPTER

Investigating Chemical Reactions 9 Key Ideas Chemical reactions are processes that involve chemical change and obey the Law of Conservation of Mass. Chemical equations are used to describe chemical reactions. There are six common types of chemical reactions. Chemists are able to predict the products of common reactions. The rate of a chemical reaction is affected by various factors. CHAPTER

Chemical reactions are simply processes that involve chemical change. A chemical change is one in which new substances are formed. A chemical equation uses chemical formulas to describe the chemicals that react (the reactants) and those that are produced (the products). Mass is conserved in a chemical reaction (Law of Conservation of Mass). This is true since the number of atoms of each element is conserved in a chemical reaction. Describing Chemical Compounds 9.1 VOCABULARY chemical reactions chemical equation reactants products Law of Conservation of Mass

Writing and Balancing Chemical Equations 9.2 VOCABULARY skeleton equation balanced equation Chemical equations are used to describe chemical reactions. Coefficients in a chemical equation describe the number of molecules of each compound or element, whereas subscripts describe the number of atoms of each element. Balancing an equation involves changing the coefficients as required throughout the equation so that atoms are conserved. Subscripts are never changed. For example when the number of atoms of the reactant element(s) are the same as the number of atoms of the product element(s), the equation is balanced.

Types of Chemical Reactions 9.3 VOCABULARY synthesis reaction decomposition reaction single replacement reaction double replacement reaction acid–base neutralization reaction combustion reaction There are six types of chemical reactions. Patterns exist in chemical reactions that allow most to be classified as one of six types:

Types of Chemical Reactions 9.3 VOCABULARY synthesis reaction decomposition reaction single replacement reaction double replacement reaction acid–base neutralization reaction combustion reaction Given the reactants for a reaction, you can often predict the products that will form, as well as the relative amounts of reactants and products based on the patterns shown on the previous screen. For example: Predicting the reactants or products of a reaction requires an understanding of reaction types, chemical formula writing, and balancing equations.

Rates of Chemical Reactions 9.4 VOCABULARY reaction rate kinetic molecular theory collision theory catalyst Some chemical reactions are slow, some are fast. For example a car rusting is slow; a matchstick burning is fast. The reaction rate of a chemical reaction is the amount of reactant consumed per unit time or the amount of product formed per unit time. It is the “speed” of the reaction.

Reaction rate is explained by the collision theory, which states that molecules must collide in order to react. Collisions must also be effective, which means that they must have sufficient energy for a reaction to occur. Reaction rate can be increased by: 1.increasing the concentration of reactants3. increasing the temperature 2.increasing the surface area of reactants4. adding a catalyst Rates of Chemical Reactions 9.4 VOCABULARY reaction rate kinetic molecular theory collision theory catalyst