Question

multiple choice. choose the one alternative that best completes the statement or answers the question. 24) which of the following statements about compounds is true? a) a substance that is not as common as pure elements. b) a substance composed of two or more elements in fixed, definite proportions. c) a substance that cannot be broken down into simpler substances. d) a pure substance that has variable composition throughout. e) none of the above 25) physical properties are: a) those that cause atoms and molecules to change. b) those that a substance displays without changing its composition. c) those that a substance displays only through changing its composition. d) identical for all solid matter. e) none of the above 26) which statement below best describes the process of the paint on a vehicle fading over time? a) chemical change because the paint molecules are changing composition. b) chemical change because the paint molecules are changing phases. c) physical change because the paint molecules have risen to the surface of the clear coat finish. d) physical change because the paint molecules are still paint molecules. e) none of the above 27) which state of matter has atomic spacing that is close together and indefinite shape? a) plasma b) solid c) gas d) liquid e) none of the above 28) what is the value of 27°c on the kelvin temperature scale? a) 300 b) 81 c) 273 d) 246 e) none of the above 29) what is the specific heat (j/g°c) of a metal object whose temperature increases by 3.0°c when 175 g of metal was heated with 38.5 j? a) 4.18 b) 1.4 c) 0.15 d) 0.73 e) none of the above 30) how many calories are there in a 255 calorie snack bar? a) 1.07 x 10³ b) 2.55 x 10⁵ c) 1 x 10³ d) 60.9 e) none of the above

Explanation:

Step1: Recall compound definition

A compound is a substance composed of two or more pure elements in fixed, definite proportions.

Step2: Analyze each option for question 24

• Option A: Incorrect, compounds are common.
• Option B: Incorrect, pure elements are different from compounds.
• Option C: Correct, matches compound definition.
• Option D: Incorrect, pure substances can be elements or compounds, and compounds can be broken - down.
• Option E: Incorrect as C is correct.

Step3: Recall physical property definition for question 25

Physical properties are those that a substance displays without changing its composition. Option C is correct.

Step4: Analyze paint - fading for question 26

Paint fading is a physical change because the paint molecules are still paint molecules. Option E is correct.

Step5: Recall states of matter for question 27

Liquids have atomic spacing that is close together and indefinite shape. Option D is correct.

Step6: Use temperature conversion formula for question 28

The conversion formula from Celsius to Kelvin is $K = ^{\circ}C+ 273$. So, $27 + 273=300$ K. Option A is correct.

Step7: Use specific - heat formula for question 29

The specific - heat formula is $q = mc\Delta T$, where $q$ is heat, $m$ is mass, $c$ is specific heat, and $\Delta T$ is temperature change. Rearranging for $c$ gives $c=\frac{q}{m\Delta T}$. Substituting $q = 38.5$ J, $m = 175$ g, and $\Delta T=3.0^{\circ}C$: $c=\frac{38.5}{175\times3.0}\approx0.073$ J/g°C. Option E is correct as none of the given options match.

Step8: Recall calorie - Calorie conversion for question 30

1 Calorie = 1000 calories. So, 255 Calories = $255\times1000 = 2.55\times10^{5}$ calories. Option B is correct.

Answer:

1. C. A substance composed of two or more pure elements in fixed, definite proportions.
2. C. those that a substance displays without changing its composition.
3. E. none of the above
4. D. liquid
5. A. 300
6. E. none of the above
7. B. $2.55\times 10^{5}$