Chemical reactions

In a heterogeneous mixture, the substances

• Can be physically separated

• are chemically combined

• can only be separated by chemical processes

• break down into new substances

Which statement is true?

• A solution is a pure substance

• A solution is a mixture

• A solvent is dissolved in the solute

• A solution has the same properties as a colloid

Milk and salt water are both mixtures. Which of the two are colloids?

• Milk

• Salt water

• Both

• Neither

Which of the following is an example of a chemical change?

• Breaking a rock

• burning a candle

• mixing butter and sugar

• adding food coloring to water

In general, what happens to the rate of reaction when you decrease the temperature of a chemical reaction?

• It decreases

• It increases

• It is unaffected

• it increases and then decreases

Burning a log is an example of

• An endothermic reaction

• a solution

• a catalyst

• an exothermic reaction

All chemical changes result in...

In the chemical equation shown, what are the reactants?

 $4\ Al\ +\ 3\ O_{2\ }\rightarrow2AL_2O_3$  

•  $Al_2O_{3\ }and\ Al$  

•  $Al_2O_3$  

•  $Al\ and\ O_2$  

•  $Al_2O_3\ and\ O_2$  

You run an experiment where two substances react chemically in a closed system. You run the same experiment in an open system. How would the masses of the products in each experiment compare?

• The mass of the closed system would be greater

• The mass of the open system would be greater

• The masses would be the same

Which of the following statements about synthetic materials is true

• Synthetic materials are never harmful to the envornment

• Synthetic materials are pure substances found in nature

• Synthetic materials have properties that are different from the properties of the nature materials used to produce them

• Synthetic materials are not different from natural materials