Science T1 Wk 7 (CA) PDF

29. Define chemical energy. Chemical energy is energy that is stored in chemical bonds. 30. What does the chemical energy stored in a molecule depend on? The chemical energy stored in molecule depends on the energy of all of the bonds it contains. 31. What causes the energy exchange in a ch...

29. Define chemical energy. Chemical energy is energy that is stored in chemical bonds. 30. What does the chemical energy stored in a molecule depend on? The chemical energy stored in molecule depends on the energy of all of the bonds it contains. 31. What causes the energy exchange in a chemical reactions? All chemical reactions involve changes in energy because bonds are broken and new bonds are formed. 32. Relate energy to breaking and forming chemical bonds. Energy is required to break chemical bonds in the reactants so that atoms can be rearranged. Energy is released when new chemical bonds form between atoms to make products. 33. What is the relationship between the energy of a chemical reaction and the energies of the substances involved in that reaction? The energy released or gained by a chemical reaction is the difference between the energies of the bonds that form and the energies of the bonds that break. 34. Define exothermic reaction. An exothermic reaction is a reaction that gives off heat. 35. What is the evidence of an exothermic reaction? An increase in the temperature of the surroundings is evidence of an exothermic reaction. 36. Define endothermic reaction. An endothermic reaction is a reaction that takes in heat. 37. What is the evidence of an endothermic reaction? Reactions cause a decrease in the temperature of their surroundings. 38. Define reaction rate. A reaction rate is a measure of how fast a reaction occurs. 39. Define concentration. The concentration of a substance in a mixture is defined as the amount of that substance in a given volume of solution. (A dilute solution is a solution with low concentration of solute, while a concentrated solution is a solution with high concentration of solute.) 40.Give an example of a) a fast chemical reaction b) a slow chemical reaction. a) The reaction between methane and oxygen is a fast chemical reaction. b) The reaction between iron and oxygen (rust) is a slow chemical reaction. 41. Are all exothermic reactions faster than endothermic reactions? Explain. Reaction rates vary widely, but they do not depend on whether a reaction is exothermic or endothermic. Both exothermic and endothermic reactions may be fast or slow. 42. List three factors that increase the rate of a reaction. These factors include temperature, particle size, the concentration of reactants, and agitation. 43. How does the temperature affect the rate of a reaction? Give an example. The rate of a chemical reaction usually increases as the temperature increases. Example: When cooking, increasing the temperature makes the food cook faster, and decreasing the temperature makes the food cook slower. 44. How does the contact surface area affect the rate of a reaction? Give an example. Reactions tend to be faster when the size of the reactant pieces is smaller. Crushing and cutting a reactant will decrease the particle size and increase the area of the contact surface between the reactants. Example: a large log will burn slowly because much of the wood is on the inside but chopping the log into smaller pieces will make it burn faster because more of the wood is in contact with the oxygen in air. 1. What do all chemical changes have in common? All chemical changes result in the formation of new substances. 2. What does the energy change during a chemical reaction depend on? When heat is released during a chemical reaction, the temperature of the surroundings increases. When heat is taken in, the temperature of the surroundings decreases. 3. Why is energy in the form of light evidence of a chemical reaction? Some chemical reactions release energy in the form of light. 4. How do changes in state and colour provide evidence of a chemical reaction? The products of a reaction may be in a different state or have a different colour than the reactants have. Therefore, observing these changes is evidence of a chemical reaction. 5. How do the chemical and physical properties of reactants compare to those of the products? The reactants and products may have some similar physical properties. The chemical properties of the reactants are different from those of the products and indicate whether a chemical reaction has occurred or not. 6. What is one example of how chemists have increased the diversity of matter? Chemists have increased the diversity of matter by making new substances, such as plastics, that do not exist in nature. 7. [G] Define chemical change. A chemical change is a change in which one or more new substances are formed. 8. [G] Define chemical reaction. A chemical reaction is the process in which atoms in given substances rearrange into new substances. 9. [G] Define reactant. A reactant is a starting substance that undergoes a chemical change in a chemical reaction. 10. [G] Define product. A product is a substance that results from a chemical reaction. 11. [G] What are some examples that provide evidence of a chemical reaction? Evidence of a chemical reaction include temperature changes, light production, change of state, change of color, and change in chemical properties. 12. How does a chemical equation show the reactants and products of a reaction? A chemical equation uses chemical formulas. The reactants are on the left side of the equation, and the products are on the right side. 13. When can ionic equations be used to represent a reaction? Ionic equations can be used when at least one of the reactants or products is an ionic compound that is dissolved in water. 14. How can you tell that a chemical equation is balanced? For each element, the number of atoms in the reactants equals their number in the products. 15. How can you show that mass is conserved in a reaction? Comparing the total mass of all of the reactants to the total mass of all of the products will show that the mass does not change in a reaction. 16. Why are whole numbers used to balance chemical equations? Chemical equations represent what happens to the particles during a chemical reaction. Since a fraction of a molecule will not react, only whole numbers must be used. 17. [G] Write the chemical equation for the reaction of decomposition of water into hydrogen and oxygen. 2𝐻2 𝑂 → 2𝐻2 + 𝑂2 18. [G] What information does reading a chemical equation provide? the elements involved in the reaction, the reactants, the products, the states of the reactants and products 19. [G] How are the states of the reactants and products indicated in chemical reactions? State Symbol Solid (s) Liquid (l) Gas (g) Dissolved in water (aqueous) (aq) 20. [G] Write the ionic equation of the following reaction: Zn(s) + Cu𝑆𝑂4 (aq) → Cu(s) + Zn𝑆𝑂4 (aq) 𝑍𝑛(𝑠) + 𝐶𝑢+2 (𝑎𝑞) + 𝑆𝑂4−2 (𝑎𝑞) → 𝐶𝑢(𝑠) + 𝑍𝑛+2 (𝑎𝑞) + 𝑆𝑂4−2 (𝑎𝑞) 21. [G] Define balanced equation. A balanced equation is a chemical equation where the number of atoms of each element is the same in the reactants and the products. 22. [G] Compare the mass of products to that of reactants in a balanced chemical equation. In a balanced chemical equation, the total mass of the products equals the total mass of the reactants. 23. [G] How can you balance a chemical equation? Add coefficients one at a time to balance each element. 24. What is the source of energy that is released by rotting leaves? The energy is released by the chemical reactions that cause the leaves to rot. 25. How can you tell if a reaction is exothermic or endothermic? A reaction is exothermic when it releases heat, making its surroundings warmer. It is endothermic when it takes in heat, making its surroundings cooler. 26. How does the concentration of reactants change over time for a reaction that has a fast reaction rate? The amount of reactants will decrease quickly as they change into products. 27. Why are catalysts not reactants? Catalysts are not used up during reactions. 28. [G] Define chemical energy. Chemical energy is energy that is stored in chemical bonds. 29. [G] What causes the energy exchange in a chemical reaction? The breaking of bonds and the formation of new ones 30. [G] Define exothermic reaction. An exothermic reaction is a reaction that gives off heat. 31. [G] Define endothermic reaction. An endothermic reaction is a reaction that takes in heat. 32. [G] Define reaction rate. A reaction rate is a measure of how fast a reaction occurs. 33. [G] List three factors that increase the rate of a reaction. increasing the temperature, increasing the concentration of the reactants, agitation, using a catalyst