# Which of the following procedures involves a physical change in one of the substances? pls help!?

creating salt by reacting sodium metal and chlorine gas

1. Which of the following procedures involves a physical change in one of the substances?
separating an oil from solution by cooling it: physical
(* creating salt by reacting sodium metal and chlorine gas: chemical; allowing a nail to rust: chemical; building a model rocket propelled by mixing baking soda and vinegar: chemical)

2. Which of the following is a homogenous mixture of two or more pure substances?
alcohol
(* they are all homogeneous, but only alcohol is made up of pure substances)

3. A container has the dimensions of 30 cm x 50 mm x 0.2 m. The density of its contents is 2.5 g/cm3. What is the mass of the substance in kilograms? (D = m/V)
7.5 kg
(* M = 3,000 (2.5) = 7,500 g = 7.5 kg)

4. A chemical reaction gives off 2,100 kJ of heat energy. About how many calories is this? (1 calorie = 4.18 Joules)
5.0 x 10^5 calories
(* kilojoule (kJ), an SI unit of energy equal to 10^3 joules; 2100 / 4.18 = 502.392344 and then move the decimal point 2 times to the left. That is another 10^2 so 10^3 + 10^2 = 10^5)

5. A material has a density of 8.9 g/cm3. You have 3 cm^3 of the substance. What is the material’s mass in grams?
27 g
(* M = 3(8.9) = 26.7 g; when rounded is 27 g)

1. allowing oil to seperate is a physical change. The oil didn’t turn into anything else by reacting

2. alcohol is homogeneous. Alcohol and water, they are misscible (not sure of the spelling)

3. none of those are true. A kilojoule is 1000 joules. all of the values you gave were under 2215.4 joules In other words they were all under 2.215 kilojoules

But of course if you mean 2.1 kilojoules and had a typing mistake then the answer is 5.0 x 103 calories

4. The material’s mass should be actually 26.7 grams but according to the values you gave it would be closest to 27 grams