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Learning Goals – I will be able to…. Understand how particles in a mixture react with each other and the main factors that speed up or slow down a chemical reaction Tell a homogeneous from a heterogeneous reaction by looking at the physical states of reactants and products
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Learning Goals – I will be able to… • Understand how particles in a mixture react with each other and the main factors that speed up or slow down a chemical reaction • Tell a homogeneous from a heterogeneous reaction by looking at the physical states of reactants and products • Recognize/define chemical equilibrium
A. How Chemical Reactions Occur • Collision model – molecules must collide in order for a reaction to occur Speeding up a reaction means having more collisions. How can we have more collisions between molecules?
Which solution is more concentrated? A or B? A or C? B or C? C A B Which solution will have more collisions between molecules?
B. Conditions That Affect Reaction Rates • Concentration – increases rate because more molecules lead to more collisions • Temperature – increases rate • Why? This is why a fever helps you fight disease – it increases the rate of metabolic reactions needed to make substances that fight disease!
Effect of Surface Area on Reaction Rates Ex.: HCl reacting with a piece of Mg
B. Conditions That Affect Reaction Rates • Activation energy – minimum energy required for a reaction to occur
B. Conditions That Affect Reaction Rates • Catalyst – a substance that speeds up a reaction without being consumed • Enzyme – catalyst in a biological system
Flashback from Biology:How Enzymes Catalyze Metabolic Reactions
C. Homogeneous vs. Heterogeneous Reactions • Homogeneous reaction – all reactants and products are in one phase • Gas • Solution
C. Homogeneous vs. Heterogeneous Reactions • Heterogeneous reaction – reactants/products in two or more phases
D. The Equilibrium Condition • Equilibrium – the exact balancing of two processes, one of which is the opposite of the other
Chemical Equilibrium • Chemical equilibrium – a dynamic state where the concentrations of all reactants and products remain constant • Chemical reactions are reversible; the forward and reverse reactions eventually “cancel out” each other: H2O + CO CO2 + H2
Although time continues to pass, the numbers of reactant and product molecules are the same as in (c). No further changes are seen as time continues to pass. The system has reached equilibrium. The reaction continues as time passes and more reactants are changed to products. The reaction begins to occur, and some products (H2 and CO2) are formed. Equal numbers of moles of H2O and CO are mixed in a closed container. E. Chemical Equilibrium: A Dynamic Condition
E. Chemical Equilibrium: A Dynamic Condition • Why does equilibrium occur?
Check yourself for understanding: • Answer the questions on your ch. 7 / 17.1 Review w.s. • Discuss your answers with a partner